We Keep Coding

I want to add arrays without changing the order

class Solution {
public void moveZeroes(int[] nums, int[] arr) {
for(int i =0; i<=nums.length-1; i++){
if(nums[i]!=0) continue;
else{
// here will be the code
}
}
}
}
is there any method or function (or any other help) that I could write in else block that would add another array in the end of nums array without changing the order of numbers and code above. The code above is for adding two arrays containing non zero arrays, if an array contains zero then delete the zero without changing the order.
Example- nums =1,9,2,0,5 ; arr= 0,4,2,7,0
Output - 1,9,2,5,4,2,7

Updated
You can do the concatenation of arrays and filter the 0s out in a single line using streams. Thanks to #Eritrean for reminding me this. You can just modify your moveZeroes function like this:
public static int[] moveZeroes(int[] nums, int[] arr) {
return Stream.of(nums,arr).flatMapToInt(Arrays::stream).filter(x-> x!=0).toArray();
}
Old Answer
You can concatenate the two arrays and then just filter the 0s out from the resulting array using streams.
You can concatenate arrays as below:
int[] result = new int[nums.length+arr.length];
System.arraycopy(nums, 0, result, 0, nums.length);
System.arraycopy(arr, 0, result, nums.length, arr.length);
The `System.arraycopy() parameters works as follows:
The first one takes the source array, second one takes source array start Index, then destination array, destination array start index, destination array upto index+1 which is here the source array length.
After that just use stream and filter to get your expected array:
Arrays.stream(result)
.filter(x -> x!=0)
.toArray();
The corresponding moveZero function will look something like this:
public int[] moveZeroes(int[] nums, int[] arr) {
int[] result = new int[nums.length+arr.length];
System.arraycopy(nums, 0, result, 0, nums.length);
System.arraycopy(arr, 0, result, nums.length, arr.length);
return Arrays.stream(result)
.filter(x -> x!=0)
.toArray();
}
The answer is what you expected:
[1, 9, 2, 5, 4, 2, 7]

If you should use only arrays you should know first the number of non zero elements in both of the arrays in order to determine the size of the output array. After that you just need to iterate over the arrays and to add them in a new array
class Solution {
public int[] moveZeroes(int[] nums, int[] arr) {
int nonZeroCount = 0;
for (int n: nums) {
if (n != 0) {
nonZeroCount++;
}
}
for (int n: arr) {
if (n != 0) {
nonZeroCount++;
}
}
int[] result = new int[nonZeroCount];
int i = 0;
for (int n: nums) {
if (n != 0) {
result[i++] = n;
}
}
for (int n: arr) {
if (n != 0) {
result[i++] = n;
}
}
return result;
}
}

You should create a new result array with max length of nums.length+arr.length then in the else loop through the add the values to this result array then repeat the same for arr.
public void moveZeroes(int[] nums, int[] arr) {
int result[] = new int[nums.length+arr.length];
int index =0;
for(int i =0; i<=nums.length-1; i++){
if(nums[i]!=0) continue;
else{
// here will be the code
result[index++] = nums[i];
}
}
for(int i =0; i<=arr.length-1; i++){
if(arr[i]!=0) continue;
else{
// here will be the code
result[index++] = arr[i];
}
}
}
I haven't tested it. But this should give you some idea.

I can use it if you want plus to array:
int[] newArr = new int[arr.length + nums.length];
int x = 0;
for (int i = 0; i < nums.length + arr.length; i++) {
if (i < nums.length) {
if (nums[i] == 0) {
x++;
continue;
} else {
newArr[i - x] = nums[i];
}
} else {
if (arr[i - nums.length] == 0) {
x++;
continue;
} else {
newArr[i - x] = arr[i - nums.length];
}
}
}
int[] arrs = new int[arr.length + nums.length-x];
for (int i = 0; i < arrs.length; i++) {
arrs[i]=newArr[i];
}
return arrs;

In Java an array is immutable structure: you can't modify length of the array.
public static void main(String... args) {
int[] nums = { 1, 9, 2, 0, 5 };
int[] arr = { 0, 4, 2, 7, 0 };
int[] res = moveZeroes(nums, arr);
}
public static int[] moveZeroes(int[] nums, int[] arr) {
int[] res = new int[calcNonZeroLength(nums) + calcNonZeroLength(arr)];
int j = 0;
for (int[] curArr : Arrays.asList(nums, arr))
for (int i = 0; i < curArr.length; i++)
if (curArr[i] != 0)
res[j++] = curArr[i];
return res;
}
private static int calcNonZeroLength(int[] arr) {
int count = 0;
for (int i = 0; i < arr.length; i++)
if (arr[i] != 0)
count++;
return count;
}

you need to add a return type of array int[] to your method
create a counter variable to keep track of number of elements you have
Create an empty array with the length of nums.length + arr.length (your array may not have zero values). iterate over each array and check values if it's not zero then add to the temp array and increase the counter.
create a new array according to counter to remove the zero elements of temp array.
public int[] moveZeroes(int[] nums, int[] arr) {
int[] temp = new int[nums.length + arr.length];
int count = 0;
for (int i = 0; i < nums.length; i++) {
if(nums[i] != 0) {
temp[count++] = nums[i];
}
}
for (int i = 0; i < arr.length; i++) {
if(arr[i] != 0) {
temp[count++] = arr[i];
}
}
int [] result = new int[count];
for (int i = 0; i < result.length; i++) {
result[i] = temp[i];
}
return result;
}

here is a full example for you
'''
public static int[] removeTheElement(int[] arr,
int index)
{
// If the array is empty
// or the index is not in array range
// return the original array
if (arr == null
|| index < 0
|| index >= arr.length) {
return arr;
}
// Create another array of size one less
int[] anotherArray = new int[arr.length - 1];
// Copy the elements except the index
// from original array to the other array
for (int i = 0, k = 0; i < arr.length; i++) {
// if the index is
// the removal element index
if (i == index) {
continue;
}
// if the index is not
// the removal element index
anotherArray[k++] = arr[i];
}
// return the resultant array
return anotherArray;
}
public void moveZeroes(int[] nums, int[] arr) {
for(int i =0; i<=nums.length-1; i++){
if(nums[i]!=0) continue;
else{
nums = removeTheElement( nums , nums[i]);
}
}
}

Return indices of the two numbers such that they add up to a specific target

I have the below question I am trying to solve:
Given an array of integers, return indices of the two numbers such that they add up to a specific target.
I have the below array as input - [2, 7, 11, 15] with target = 9.
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
This is my code -
import java.util.Random;
public class TwoSum {
static int[] numbers = new int[] {2, 7, 11, 15};
int[] indices = new int[numbers.length];
public static int[] returnIndices(int target, int[] inputArr) {
int[] indices = new int[2];
int randomOne = new Random().nextInt(inputArr.length);
int randomTwo = new Random().nextInt(inputArr.length);
while(true) {
if(target == inputArr[randomOne] + inputArr[randomTwo]) {
indices[0] = randomOne;
indices[1] = randomTwo;
break;
}
}
System.out.println("done");
return indices;
}
public static void main(String[] args) {
int[] output = returnIndices(9, numbers);
}
}
Is this the right way to approach my problem?

You can use a hashmap to store the first array in the following manner:
key value(index in array)
2 - 0
7 - 1
11 - 2
15 - 3
Next get the target element which is 9, and start traversing your given array from index 0.
Element at index 0 is 2 --> calculate (9-2) = 7 --> check if 7 is a key in the hashmap
Additional Note: You need to take care of the following case:
arr = [3, 2, 1, 1] target = 6 (no answer exists in this case, but by the above method, when you calculate 6-3 = 3 you get index 0 as the answer.)
But this can easily be taken care of by checking whether (target-arr[i] == arr[i]) returns true or not. If it returns true and if the hashmap has two indices stored at the key arr[i], then return it as an answer, else proceed to the next element.

There are various ways to solve this question:
Hashmap way - #mettleap answer has covered that one.
Sort-Array way - I am going to explain its pseudo code to you.
Let us take an example to see it in action first. We are given arr = [5, 2, 1, 9, 7] elements in an array, and we are to find the indices of two elements if we can make 8.
If you look closely, then you will know if we sum 3rd + last element in an array, we will get 8, which means 2 and 4 would be our answer. So How would be land there? Let us go step by step
Maintain a separate array of the same size, it will hold the indices of arr in its initial setup.
[5, 2, 1, 9, 7] = arr
[0, 1, 2, 3, 4] = index_arr
Now sort arr in increasing order, and also sort the index_arr such that index of elements in arr in their initial setup is still in place.
[1, 2, 5, 7, 9] = arr
[2, 1, 0, 4, 3] = index_arr
Use the below pseudo code:
low = 0
high = length of arr - 1
while (low < high) {
sum = arr[low] + arr[high]
if (sum == number) {}
print "index_arr[low]" and "index_arr[high]"
break the loop and exit
} else if ( sum < number ) {
low = low + 1
} else {
high = high - 1
}
}
Let us see psuedo code in action:
[1, 2, 5, 7, 9] = arr
[2, 1, 0, 4, 3] = index_arr
Iteration # 01
low = 0 and high = 4
sum = arr[0] + arr[4] = 1 + 9 = 10
10 > 8 , means 'else' will be executed high = high - 1 = 4 - 1 = 3
Iteration # 02
low = 0 and high = 3
sum = arr[0] + arr[3] = 1 + 7 = 8
8 == 8 , means first 'if' condiion will execute, and will indices and exit the loop
Time Complexity - O(n)
Space Complexity - O(n)

I have tried it in c#, It may help..
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
int[] nums = { 2, 7, 11, 15 };
int target = 9;
int[] result= TwoSumNumbers(nums, target);
}
public static int[] TwoSumNumbers(int[] nums, int target)
{
Dictionary<int, int> numsDict = new Dictionary<int, int>();
for (int i = 0; i < nums.Length; i++)
{
int num = nums[i];
if (numsDict.TryGetValue(target - num, out int index))
{
return new[] { index, i };
}
numsDict[num] = i;
}
return null;
}
}

class Solution {
public int[] twoSum(int[] nums, int target) {
int [] answer = new int[2];
Map<Integer,Integer> values = new HashMap<Integer,Integer>();
for ( int i=0; i < nums.length; i++){
values.put(nums[i],i);
}
for ( int i=0; i < nums.length; i++){
int val = target - nums[i];
Integer secondIndex = values.get(val);
if ( secondIndex != null && secondIndex != i){
answer[0] = i;
answer[1] = secondIndex;
return answer;
}
}
return answer;
}
}

C# Version
using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
namespace MyBasics
{
class ArrayIndexForTarget
{
public static void Main()
{
ArrayIndexForTarget find = new ArrayIndexForTarget();
int[] arr = new int[] { 9, 2, 3, 9, 10 };
int target = 11;
var result = find.IndexFinder(arr, target);
Console.ReadKey();
}
public int[] IndexFinder(int[]myArray,int target)
{
int[] arr = new int[2];
Dictionary<int, int> dict = new Dictionary<int, int>();
for (int p=0; p < myArray.Length; p++)
{
int numberToFind = target - myArray[p];
if (dict.ContainsValue(numberToFind))
{
arr[0] = dict.FirstOrDefault(x => x.Value == numberToFind).Key;
arr[1] = p;
return arr;
}
else
{
dict.Add(p,myArray[p]);
}
}
return arr;
}
}
}

class Solution {
function twoSum($nums, $target) {
$lenght = count($nums);
$indices = array();
for($i = 0; $i<$lenght-1; $i++){
for($j=$i+1; $j<$lenght; $j++){
if(($nums[$i]+$nums[$j]) == $target){
$indices[] = $i;
$indices[] = $j;
return $indices;
}
}
}
} }

private static int[] findNumbersToAdd(int target, int[] array) {
int[] answer = {-1, -1};
int length = array.length;
for (int i = 0; i < length; i++) {
int var1 = array[i];
for (int j = i + 1; j < length; j++) {
int var2 = array[j];
if (var1 + var2 == target) {
answer[0] = i;
answer[1] = j;
break;
}
}
}
return answer;
}

Given you aren't focused on performance I would think a brute force approach would be fine. Here is a solution using streams and records.
record IndexPair(int index1, int index2) { };
IntStream.range(0, arr.length).boxed()
.flatMap(i1 -> IntStream.range(i1, arr.length)
.filter(i2 -> arr[i1] + arr[i2] == target)
.mapToObj(i2 -> new IndexPair(i1, i2))
.forEach(ip -> ...);
If you only want one solution then you could use findAny instead of forEach.

I tried this question and implement it using HashMap in Java and it works completely fine.
public class Solution {
public int[] twoSum(final int[] A, int B) {
HashMap<Integer,Integer> hm=new HashMap<>();
int index1=Integer.MAX_VALUE;
int index2=Integer.MAX_VALUE;
int diff=0;
for(int i=0;i<A.length;i++){
diff=B-A[i];
if(hm.containsKey(diff)){
index2=i;
index1=hm.get(diff);
return new int[] {index1+1,index2+1};
}else{
if(!hm.containsKey(A[i])){
hm.put(A[i],i);
}
}
}
// If Arrays doesnt have such pairs
if(index2 == (Integer.MAX_VALUE) || index1 == (Integer.MAX_VALUE)){
return new int[] {};
}
return new int[] {index1+1,index2+1};
}
}

here is a simple solution with 2 running loops,
assuming the following
you only need 2 numbers to get to the target.
the solution exists (therefor no need to validate).
public int[] TwoSum(int[] nums, int target) {
for (int i=0; i< nums.Length; i++){
for (int j=i+1; j< nums.Length; j++){
if (nums[i] + nums[j] == target){
return new int[]{i,j};
}
}
}
return null;
}

public int[] sumofTwo(int[] numbers, int target)
{
int[] answer = new int[2];
Map<Integer,Integer> map = new HashMap<Integer,Integer>();
for(int i = 0 ; i < numbers.length ; i++)
{
if(map.containsKey(target - numbers[i]))
{
answer[0] = map.get(target - numbers[i]);
answer[1] = i;
return answer;
}
else
{
map.put(numbers[i],i);
}
}
return null;
}
}

public class Main {
public static void main(String[] args) {
int [] arr = {4,7,1,-3,2};
for(int i=0; i<arr.length-1; i++)
{
for(int j=0; j<=arr.length-2; j++)
{
if((arr[i]+arr[j+1])==6)
{
System.out.println("indices = "+"["+i +","+(j+1)+"]");
}
}
}
}
}

Array not registering added ints

I'm working on a problem on leetcode (Two Sum):
Given an array of integers, return indices of the two numbers such
that they add up to a specific target.
You may assume that each input would have exactly one solution, and
you may not use the same element twice.
Example: Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].
I tried my own solution and the array always showed [0,0]. So I tried a solution that they had after several tweeks and that still showed [0,0] when I put it in and it was the highest ranked solution. Is it me or is it leetcode?
Original Solution:
import java.util.Arrays;
public class Solution {
public int[] twoSum(int[] nums, int target) {
int[] indices = new int[2];
for(int i = 0; i < nums.length-1; i++)
{
for(int j = i+1; j < nums.length-1; j++)
{
if(target == (nums[i] + nums[j]))
{
indices[0] = i+1;
indices[1] = j+1;
}
}
}
return indices;
}
}
Leetcode Solution:
public class Solution {
public int[] twoSum(int[] nums, int target) {
int[] indices = new int[2];
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for(int i = 0; i < nums.length-1; i++)
{
if(map.containsKey(target - nums[i]))
{
indices[1] = i + 1;
indices[0] = map.get(target - nums[i]);
return indices;
}
map.put(nums[i], i + 1);
}
return indices;
}
}
I don't understand why neither of these will register ints in the indices array, it continually returns [0,0] for both solutions.

In my understanding your innerloop must not start with i+1, cause you have to check each index in your array. only if the index of the inner and outer loop match, you should skip it, cause you won't add the index with itself.
you must loop your array to the end (so i removed the -1 in the for-statement)
why are you returning i+1 and j+1 if you found a match? (so i removed this)
see my code. maybe it will be more clear, what im trying to say :-)
public class Solution {
public static void main(String[] args) {
Solution solution = new Solution();
int[] result = solution.twoSum(new int[] { 2, 7, 11, 15 }, 17);
System.out.println(result[0] + "/" + result[1]);
}
public int[] twoSum(int[] nums, int target) {
int[] indices = new int[2];
for (int i = 0; i < nums.length; i++) {
for (int j = 0; j < nums.length; j++) {
if (i == j) {
//do not use the same index for sum
continue;
}
if (target == (nums[i] + nums[j])) {
indices[0] = i;
indices[1] = j;
}
}
}
return indices;
}
}

The simplest way to loop through combinations of two within an array can be done as follows:
for(int i=0 ; i<nums.length-1 ; i++)
for(int j=i+1 ; j<nums.length ; j++)
if(nums[i]+nums[j]==target)
return new int[] {i, j};
return null; //in case there's no such case

Brute forcing the twosum algorithm

The twosum question is:
Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].
I'm learning java and I'm going through some leetcode problems. I'm trying to come up with a brute force solution before I code for efficiency but my code won't seem to compile:
public class TwoSum
{
//static int[] arraynums = new int[]{2, 7, 11, 15};
//static int target = 9;
//public static void main(String args[])
//{
//TwoSum name = new TwoSum();
//name.twoSums(arraynums, target);
//}
public int twoSums(int[] nums, int target)
{
int sum = 0;
for (int i = 0; i < nums.length; i++)
{
for (int j = 0; j < nums.length; j++)
{
sum = nums[i] + nums[j];
if (sum == target)
{
System.out.println(i + " " + j);
return new int[] {i,j};
}
}
}
return new int[] {};
}
}
I know I need a return statement but I'm not sure what I should return and I'm also not sure if my main method is required.

#Alfabravo is right. you need to return an array of integer. If you don't want to return anything. just use
public void twoSum(int[] nums, int target)

You're on the right track!
In regards to adding a return statement, just add it after the println statement.
...
System.out.println(i + " " + j);
return new int[] {i,j};
...
although you need to check that i and j are not equal as they will point to the same number in nums if they are. Unless that isn't a requirement of the question. If it is you could add something like
if (sum == target && i != j)
good luck.

For leetCode you just need to complete the codes and no need to add a main function.
For your twoSum method you need to return an array with type int which contains the index of elements.
You can test like this:
public static void main(String args[]) {
int[] testData = {2, 7, 11, 15};
int target = 9;
TwoSum ts = new TwoSum();
int[] result = ts.twoSum(testData, target);
for (int i = 0; i < result.length; i++) {
System.out.println(result[i]);
}
}

public class Solution {
public int[] twoSum(int[] num, int target) {
// Take an array and the target number as parameter
// Initialize the variables
int length = num.length;
int index1 = 0;
int index2 = 0;
int i;
int j;
for (i=0; i<length; i++) {
// First loop, i starts at num[0] which is the first element in array
for (j=i+1; j<length; j++){
// Second loop, j starts at num[1], the second element
if (num[i] + num[j] == target){
// If they are equal return the index
index1 = i;
index2 = j;
}
}
}
// The result should be an array contains 2 indices
int[] result = new int[] {index1, index2};
return result;
}
}
Loop through each element x and find if there is another value that equals to target−x.

Just a small mistake when you're iterating in the next loop, just add j = i + 1. That will do it.
public int[] twoSum(int[] nums, int target) {
for(int i = 0; i < nums.length; i++){
for(int j = i + 1; j < nums.length; j++){
if (nums[i] + nums[j] == target){
return new int[] { i,j };
}
}
}
return new int[] {};
}

class Solution {
public int[] twoSum(int[] numbers, int target) {
int first = 0, sec = numbers.length-1;
while(first!=sec){
if((numbers[first]+numbers[sec])==target)
break;
else if((numbers[first]+numbers[sec])>target)
sec--;
else
first++;
}
int res[] = new int[2];
res[0] = first+1;
res[1] = sec+1;
return res;
}
}

how to print non repeated numbers from integer array using java and without using predefined api's? [duplicate]

I was asked to write my own implementation to remove duplicated values in an array. Here is what I have created. But after tests with 1,000,000 elements it took very long time to finish. Is there something that I can do to improve my algorithm or any bugs to remove ?
I need to write my own implementation - not to use Set, HashSet etc. Or any other tools such as iterators. Simply an array to remove duplicates.
public static int[] removeDuplicates(int[] arr) {
int end = arr.length;
for (int i = 0; i < end; i++) {
for (int j = i + 1; j < end; j++) {
if (arr[i] == arr[j]) {
int shiftLeft = j;
for (int k = j+1; k < end; k++, shiftLeft++) {
arr[shiftLeft] = arr[k];
}
end--;
j--;
}
}
}
int[] whitelist = new int[end];
for(int i = 0; i < end; i++){
whitelist[i] = arr[i];
}
return whitelist;
}

you can take the help of Set collection
int end = arr.length;
Set<Integer> set = new HashSet<Integer>();
for(int i = 0; i < end; i++){
set.add(arr[i]);
}
now if you will iterate through this set, it will contain only unique values. Iterating code is like this :
Iterator it = set.iterator();
while(it.hasNext()) {
System.out.println(it.next());
}

If you are allowed to use Java 8 streams:
Arrays.stream(arr).distinct().toArray();

Note: I am assuming the array is sorted.
Code:
int[] input = new int[]{1, 1, 3, 7, 7, 8, 9, 9, 9, 10};
int current = input[0];
boolean found = false;
for (int i = 0; i < input.length; i++) {
if (current == input[i] && !found) {
found = true;
} else if (current != input[i]) {
System.out.print(" " + current);
current = input[i];
found = false;
}
}
System.out.print(" " + current);
output:
1 3 7 8 9 10

Slight modification to the original code itself, by removing the innermost for loop.
public static int[] removeDuplicates(int[] arr){
int end = arr.length;
for (int i = 0; i < end; i++) {
for (int j = i + 1; j < end; j++) {
if (arr[i] == arr[j]) {
/*int shiftLeft = j;
for (int k = j+1; k < end; k++, shiftLeft++) {
arr[shiftLeft] = arr[k];
}*/
arr[j] = arr[end-1];
end--;
j--;
}
}
}
int[] whitelist = new int[end];
/*for(int i = 0; i < end; i++){
whitelist[i] = arr[i];
}*/
System.arraycopy(arr, 0, whitelist, 0, end);
return whitelist;
}

There exists many solution of this problem.
The sort approach
You sort your array and resolve only unique items
The set approach
You declare a HashSet where you put all item then you have only unique ones.
You create a boolean array that represent the items all ready returned, (this depend on your data in the array).
If you deal with large amount of data i would pick the 1. solution. As you do not allocate additional memory and sorting is quite fast. For small set of data the complexity would be n^2 but for large i will be n log n.

Since you can assume the range is between 0-1000 there is a very simple and efficient solution
//Throws an exception if values are not in the range of 0-1000
public static int[] removeDuplicates(int[] arr) {
boolean[] set = new boolean[1001]; //values must default to false
int totalItems = 0;
for (int i = 0; i < arr.length; ++i) {
if (!set[arr[i]]) {
set[arr[i]] = true;
totalItems++;
}
}
int[] ret = new int[totalItems];
int c = 0;
for (int i = 0; i < set.length; ++i) {
if (set[i]) {
ret[c++] = i;
}
}
return ret;
}
This runs in linear time O(n). Caveat: the returned array is sorted so if that is illegal then this answer is invalid.

class Demo
{
public static void main(String[] args)
{
int a[]={3,2,1,4,2,1};
System.out.print("Before Sorting:");
for (int i=0;i<a.length; i++ )
{
System.out.print(a[i]+"\t");
}
System.out.print ("\nAfter Sorting:");
//sorting the elements
for(int i=0;i<a.length;i++)
{
for(int j=i;j<a.length;j++)
{
if(a[i]>a[j])
{
int temp=a[i];
a[i]=a[j];
a[j]=temp;
}
}
}
//After sorting
for(int i=0;i<a.length;i++)
{
System.out.print(a[i]+"\t");
}
System.out.print("\nAfter removing duplicates:");
int b=0;
a[b]=a[0];
for(int i=0;i<a.length;i++)
{
if (a[b]!=a[i])
{
b++;
a[b]=a[i];
}
}
for (int i=0;i<=b;i++ )
{
System.out.print(a[i]+"\t");
}
}
}
OUTPUT:Before Sortng:3 2 1 4 2 1 After Sorting:1 1 2 2 3 4
Removing Duplicates:1 2 3 4

Since this question is still getting a lot of attention, I decided to answer it by copying this answer from Code Review.SE:
You're following the same philosophy as the bubble sort, which is
very, very, very slow. Have you tried this?:
Sort your unordered array with quicksort. Quicksort is much faster
than bubble sort (I know, you are not sorting, but the algorithm you
follow is almost the same as bubble sort to traverse the array).
Then start removing duplicates (repeated values will be next to each
other). In a for loop you could have two indices: source and
destination. (On each loop you copy source to destination unless they
are the same, and increment both by 1). Every time you find a
duplicate you increment source (and don't perform the copy).
#morgano

import java.util.Arrays;
public class Practice {
public static void main(String[] args) {
int a[] = { 1, 3, 3, 4, 2, 1, 5, 6, 7, 7, 8, 10 };
Arrays.sort(a);
int j = 0;
for (int i = 0; i < a.length - 1; i++) {
if (a[i] != a[i + 1]) {
a[j] = a[i];
j++;
}
}
a[j] = a[a.length - 1];
for (int i = 0; i <= j; i++) {
System.out.println(a[i]);
}
}
}
**This is the most simplest way**

What if you create two boolean arrays: 1 for negative values and 1 for positive values and init it all on false.
Then you cycle thorugh the input array and lookup in the arrays if you've encoutered the value already.
If not, you add it to the output array and mark it as already used.

package com.pari.practice;
import java.util.HashSet;
import java.util.Iterator;
import com.pari.sort.Sort;
public class RemoveDuplicates {
/**
* brute force- o(N square)
*
* #param input
* #return
*/
public static int[] removeDups(int[] input){
boolean[] isSame = new boolean[input.length];
int sameNums = 0;
for( int i = 0; i < input.length; i++ ){
for( int j = i+1; j < input.length; j++){
if( input[j] == input[i] ){ //compare same
isSame[j] = true;
sameNums++;
}
}
}
//compact the array into the result.
int[] result = new int[input.length-sameNums];
int count = 0;
for( int i = 0; i < input.length; i++ ){
if( isSame[i] == true) {
continue;
}
else{
result[count] = input[i];
count++;
}
}
return result;
}
/**
* set - o(N)
* does not guarantee order of elements returned - set property
*
* #param input
* #return
*/
public static int[] removeDups1(int[] input){
HashSet myset = new HashSet();
for( int i = 0; i < input.length; i++ ){
myset.add(input[i]);
}
//compact the array into the result.
int[] result = new int[myset.size()];
Iterator setitr = myset.iterator();
int count = 0;
while( setitr.hasNext() ){
result[count] = (int) setitr.next();
count++;
}
return result;
}
/**
* quicksort - o(Nlogn)
*
* #param input
* #return
*/
public static int[] removeDups2(int[] input){
Sort st = new Sort();
st.quickSort(input, 0, input.length-1); //input is sorted
//compact the array into the result.
int[] intermediateResult = new int[input.length];
int count = 0;
int prev = Integer.MIN_VALUE;
for( int i = 0; i < input.length; i++ ){
if( input[i] != prev ){
intermediateResult[count] = input[i];
count++;
}
prev = input[i];
}
int[] result = new int[count];
System.arraycopy(intermediateResult, 0, result, 0, count);
return result;
}
public static void printArray(int[] input){
for( int i = 0; i < input.length; i++ ){
System.out.print(input[i] + " ");
}
}
public static void main(String[] args){
int[] input = {5,6,8,0,1,2,5,9,11,0};
RemoveDuplicates.printArray(RemoveDuplicates.removeDups(input));
System.out.println();
RemoveDuplicates.printArray(RemoveDuplicates.removeDups1(input));
System.out.println();
RemoveDuplicates.printArray(RemoveDuplicates.removeDups2(input));
}
}
Output:
5 6 8 0 1 2 9 11
0 1 2 5 6 8 9 11
0 1 2 5 6 8 9 11
I have just written the above code for trying out. thanks.

public static int[] removeDuplicates(int[] arr){
HashSet<Integer> set = new HashSet<>();
final int len = arr.length;
//changed end to len
for(int i = 0; i < len; i++){
set.add(arr[i]);
}
int[] whitelist = new int[set.size()];
int i = 0;
for (Iterator<Integer> it = set.iterator(); it.hasNext();) {
whitelist[i++] = it.next();
}
return whitelist;
}
Runs in O(N) time instead of your O(N^3) time

Not a big fun of updating user input, however considering your constraints...
public int[] removeDup(int[] nums) {
Arrays.sort(nums);
int x = 0;
for (int i = 0; i < nums.length; i++) {
if (i == 0 || nums[i] != nums[i - 1]) {
nums[x++] = nums[i];
}
}
return Arrays.copyOf(nums, x);
}
Array sort can be easily replaced with any nlog(n) algorithm.

This is simple way to sort the elements in the array
public class DublicatesRemove {
public static void main(String args[]) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("enter size of the array");
int l = Integer.parseInt(br.readLine());
int[] a = new int[l];
// insert elements in the array logic
for (int i = 0; i < l; i++)
{
System.out.println("enter a element");
int el = Integer.parseInt(br.readLine());
a[i] = el;
}
// sorting elements in the array logic
for (int i = 0; i < l; i++)
{
for (int j = 0; j < l - 1; j++)
{
if (a[j] > a[j + 1])
{
int temp = a[j];
a[j] = a[j + 1];
a[j + 1] = temp;
}
}
}
// remove duplicate elements logic
int b = 0;
a[b] = a[0];
for (int i = 1; i < l; i++)
{
if (a[b] != a[i])
{
b++;
a[b]=a[i];
}
}
for(int i=0;i<=b;i++)
{
System.out.println(a[i]);
}
}
}

Okay, so you cannot use Set or other collections. One solution I don't see here so far is one based on the use of a Bloom filter, which essentially is an array of bits, so perhaps that passes your requirements.
The Bloom filter is a lovely and very handy technique, fast and space-efficient, that can be used to do a quick check of the existence of an element in a set without storing the set itself or the elements. It has a (typically small) false positive rate, but no false negative rate. In other words, for your question, if a Bloom filter tells you that an element hasn't been seen so far, you can be sure it hasn't. But if it says that an element has been seen, you actually need to check. This still saves a lot of time if there aren't too many duplicates in your list (for those, there is no looping to do, except in the small probability case of a false positive --you typically chose this rate based on how much space you are willing to give to the Bloom filter (rule of thumb: less than 10 bits per unique element for a false positive rate of 1%).
There are many implementations of Bloom filters, see e.g. here or here, so I won't repeat that in this answer. Let us just assume the api described in that last reference, in particular, the description of put(E e):
true if the Bloom filter's bits changed as a result of this operation. If the bits changed, this is definitely the first time object has been added to the filter. If the bits haven't changed, this might be the first time object has been added to the filter. (...)
An implementation using such a Bloom filter would then be:
public static int[] removeDuplicates(int[] arr) {
ArrayList<Integer> out = new ArrayList<>();
int n = arr.length;
BloomFilter<Integer> bf = new BloomFilter<>(...); // decide how many bits and how many hash functions to use (compromise between space and false positive rate)
for (int e : arr) {
boolean might_contain = !bf.put(e);
boolean found = false;
if (might_contain) {
// check if false positive
for (int u : out) {
if (u == e) {
found = true;
break;
}
}
}
if (!found) {
out.add(e);
}
}
return out.stream().mapToInt(i -> i).toArray();
}
Obviously, if you can alter the incoming array in place, then there is no need for an ArrayList: at the end, when you know the actual number of unique elements, just arraycopy() those.

For a sorted Array, just check the next index:
//sorted data!
public static int[] distinct(int[] arr) {
int[] temp = new int[arr.length];
int count = 0;
for (int i = 0; i < arr.length; i++) {
int current = arr[i];
if(count > 0 )
if(temp[count - 1] == current)
continue;
temp[count] = current;
count++;
}
int[] whitelist = new int[count];
System.arraycopy(temp, 0, whitelist, 0, count);
return whitelist;
}

You need to sort your array then then loop and remove duplicates. As you cannot use other tools you need to write be code yourself.
You can easily find examples of quicksort in Java on the internet (on which this example is based).
public static void main(String[] args) throws Exception {
final int[] original = new int[]{1, 1, 2, 8, 9, 8, 4, 7, 4, 9, 1};
System.out.println(Arrays.toString(original));
quicksort(original);
System.out.println(Arrays.toString(original));
final int[] unqiue = new int[original.length];
int prev = original[0];
unqiue[0] = prev;
int count = 1;
for (int i = 1; i < original.length; ++i) {
if (original[i] != prev) {
unqiue[count++] = original[i];
}
prev = original[i];
}
System.out.println(Arrays.toString(unqiue));
final int[] compressed = new int[count];
System.arraycopy(unqiue, 0, compressed, 0, count);
System.out.println(Arrays.toString(compressed));
}
private static void quicksort(final int[] values) {
if (values.length == 0) {
return;
}
quicksort(values, 0, values.length - 1);
}
private static void quicksort(final int[] values, final int low, final int high) {
int i = low, j = high;
int pivot = values[low + (high - low) / 2];
while (i <= j) {
while (values[i] < pivot) {
i++;
}
while (values[j] > pivot) {
j--;
}
if (i <= j) {
swap(values, i, j);
i++;
j--;
}
}
if (low < j) {
quicksort(values, low, j);
}
if (i < high) {
quicksort(values, i, high);
}
}
private static void swap(final int[] values, final int i, final int j) {
final int temp = values[i];
values[i] = values[j];
values[j] = temp;
}
So the process runs in 3 steps.
Sort the array - O(nlgn)
Remove duplicates - O(n)
Compact the array - O(n)
So this improves significantly on your O(n^3) approach.
Output:
[1, 1, 2, 8, 9, 8, 4, 7, 4, 9, 1]
[1, 1, 1, 2, 4, 4, 7, 8, 8, 9, 9]
[1, 2, 4, 7, 8, 9, 0, 0, 0, 0, 0]
[1, 2, 4, 7, 8, 9]
EDIT
OP states values inside array doesn't matter really. But I can assume that range is between 0-1000. This is a classic case where an O(n) sort can be used.
We create an array of size range +1, in this case 1001. We then loop over the data and increment the values on each index corresponding to the datapoint.
We can then compact the resulting array, dropping values the have not been incremented. This makes the values unique as we ignore the count.
public static void main(String[] args) throws Exception {
final int[] original = new int[]{1, 1, 2, 8, 9, 8, 4, 7, 4, 9, 1, 1000, 1000};
System.out.println(Arrays.toString(original));
final int[] buckets = new int[1001];
for (final int i : original) {
buckets[i]++;
}
final int[] unique = new int[original.length];
int count = 0;
for (int i = 0; i < buckets.length; ++i) {
if (buckets[i] > 0) {
unique[count++] = i;
}
}
final int[] compressed = new int[count];
System.arraycopy(unique, 0, compressed, 0, count);
System.out.println(Arrays.toString(compressed));
}
Output:
[1, 1, 2, 8, 9, 8, 4, 7, 4, 9, 1, 1000, 1000]
[1, 2, 4, 7, 8, 9, 1000]

public static void main(String args[]) {
int[] intarray = {1,2,3,4,5,1,2,3,4,5,1,2,3,4,5};
Set<Integer> set = new HashSet<Integer>();
for(int i : intarray) {
set.add(i);
}
Iterator<Integer> setitr = set.iterator();
for(int pos=0; pos < intarray.length; pos ++) {
if(pos < set.size()) {
intarray[pos] =setitr.next();
} else {
intarray[pos]= 0;
}
}
for(int i: intarray)
System.out.println(i);
}

I know this is kinda dead but I just wrote this for my own use. It's more or less the same as adding to a hashset and then pulling all the elements out of it. It should run in O(nlogn) worst case.
public static int[] removeDuplicates(int[] numbers) {
Entry[] entries = new Entry[numbers.length];
int size = 0;
for (int i = 0 ; i < numbers.length ; i++) {
int nextVal = numbers[i];
int index = nextVal % entries.length;
Entry e = entries[index];
if (e == null) {
entries[index] = new Entry(nextVal);
size++;
} else {
if(e.insert(nextVal)) {
size++;
}
}
}
int[] result = new int[size];
int index = 0;
for (int i = 0 ; i < entries.length ; i++) {
Entry current = entries[i];
while (current != null) {
result[i++] = current.value;
current = current.next;
}
}
return result;
}
public static class Entry {
int value;
Entry next;
Entry(int value) {
this.value = value;
}
public boolean insert(int newVal) {
Entry current = this;
Entry prev = null;
while (current != null) {
if (current.value == newVal) {
return false;
} else if(current.next != null) {
prev = current;
current = next;
}
}
prev.next = new Entry(value);
return true;
}
}

int tempvar=0; //Variable for the final array without any duplicates
int whilecount=0; //variable for while loop
while(whilecount<(nsprtable*2)-1) //nsprtable can be any number
{
//to check whether the next value is idential in case of sorted array
if(temparray[whilecount]!=temparray[whilecount+1])
{
finalarray[tempvar]=temparray[whilecount];
tempvar++;
whilecount=whilecount+1;
}
else if (temparray[whilecount]==temparray[whilecount+1])
{
finalarray[tempvar]=temparray[whilecount];
tempvar++;
whilecount=whilecount+2;
}
}
Hope this helps or solves the purpose.

package javaa;
public class UniqueElementinAnArray
{
public static void main(String[] args)
{
int[] a = {10,10,10,10,10,100};
int[] output = new int[a.length];
int count = 0;
int num = 0;
//Iterate over an array
for(int i=0; i<a.length; i++)
{
num=a[i];
boolean flag = check(output,num);
if(flag==false)
{
output[count]=num;
++count;
}
}
//print the all the elements from an array except zero's (0)
for (int i : output)
{
if(i!=0 )
System.out.print(i+" ");
}
}
/***
* If a next number from an array is already exists in unique array then return true else false
* #param arr Unique number array. Initially this array is an empty.
* #param num Number to be search in unique array. Whether it is duplicate or unique.
* #return true: If a number is already exists in an array else false
*/
public static boolean check(int[] arr, int num)
{
boolean flag = false;
for(int i=0;i<arr.length; i++)
{
if(arr[i]==num)
{
flag = true;
break;
}
}
return flag;
}
}

public static int[] removeDuplicates(int[] arr) {
int end = arr.length;
HashSet<Integer> set = new HashSet<Integer>(end);
for(int i = 0 ; i < end ; i++){
set.add(arr[i]);
}
return set.toArray();
}

You can use an auxiliary array (temp) which in indexes are numbers of main array. So the time complexity will be liner and O(n). As we want to do it without using any library, we define another array (unique) to push non-duplicate elements:
var num = [2,4,9,4,1,2,24,12,4];
let temp = [];
let unique = [];
let j = 0;
for (let i = 0; i < num.length; i++){
if (temp[num[i]] !== 1){
temp[num[i]] = 1;
unique[j++] = num[i];
}
}
console.log(unique);

If you are looking to remove duplicates using the same array and also keeping the time complexity of O(n). Then this should do the trick. Also, would only work if the array is sorted.
function removeDuplicates_sorted(arr){
let j = 0;
for(let x = 0; x < arr.length - 1; x++){
if(arr[x] != arr[x + 1]){
arr[j++] = arr[x];
}
}
arr[j++] = arr[arr.length - 1];
arr.length = j;
return arr;
}
Here is for an unsorted array, its O(n) but uses more space complexity then the sorted.
function removeDuplicates_unsorted(arr){
let map = {};
let j = 0;
for(var numbers of arr){
if(!map[numbers]){
map[numbers] = 1;
arr[j++] = numbers;
}
}
arr.length = j;
return arr;
}

Note to other readers who desire to use the Set method of solving this problem: If original ordering must be preserved, do not use HashSet as in the top result. HashSet does not guarantee the preservation of the original order, so LinkedHashSet should be used instead-this keeps track of the order in which the elements were inserted into the set and returns them in that order.

This is an interview question.
public class Test4 {
public static void main(String[] args) {
int a[] = {1, 2, 2, 3, 3, 3, 6,6,6,6,6,66,7,65};
int newlength = lengthofarraywithoutduplicates(a);
for(int i = 0 ; i < newlength ;i++) {
System.out.println(a[i]);
}//for
}//main
private static int lengthofarraywithoutduplicates(int[] a) {
int count = 1 ;
for (int i = 1; i < a.length; i++) {
int ch = a[i];
if(ch != a[i-1]) {
a[count++] = ch;
}//if
}//for
return count;
}//fix
}//end1
But, it's always better to use Stream :
int[] a = {1, 2, 2, 3, 3, 3, 6,6,6,6,6,66,7,65};
int[] array = Arrays.stream(a).distinct().toArray();
System.out.println(Arrays.toString(array));//[1, 2, 3, 6, 66, 7, 65]

How about this one, only for the sorted Array of numbers, to print the Array without duplicates, without using Set or other Collections, just an Array:
public static int[] removeDuplicates(int[] array) {
int[] nums = new int[array.length];
int addedNumber = 0;
int j = 0;
for(int i=0; i < array.length; i++) {
if (addedNumber != array[i]) {
nums[j] = array[i];
j++;
addedNumber = nums[j-1];
}
}
return Arrays.copyOf(nums, j);
}
An array of 1040 duplicated numbers processed in 33020 nanoseconds(0.033020 millisec).

public static void main(String[] args) {
Integer[] intArray = { 1, 1, 1, 2, 4, 2, 3, 5, 3, 6, 7, 3, 4, 5 };
Integer[] finalArray = removeDuplicates(intArray);
System.err.println(Arrays.asList(finalArray));
}
private static Integer[] removeDuplicates(Integer[] intArray) {
int count = 0;
Integer[] interimArray = new Integer[intArray.length];
for (int i = 0; i < intArray.length; i++) {
boolean exists = false;
for (int j = 0; j < interimArray.length; j++) {
if (interimArray[j]!=null && interimArray[j] == intArray[i]) {
exists = true;
}
}
if (!exists) {
interimArray[count] = intArray[i];
count++;
}
}
final Integer[] finalArray = new Integer[count];
System.arraycopy(interimArray, 0, finalArray, 0, count);
return finalArray;
}

I feel Android Killer's idea is great, but I just wondered if we can leverage HashMap. So I did a little experiment. And I found HashMap seems faster than HashSet.
Here is code:
int[] input = new int[1000000];
for (int i = 0; i < input.length; i++) {
Random random = new Random();
input[i] = random.nextInt(200000);
}
long startTime1 = new Date().getTime();
System.out.println("Set start time:" + startTime1);
Set<Integer> resultSet = new HashSet<Integer>();
for (int i = 0; i < input.length; i++) {
resultSet.add(input[i]);
}
long endTime1 = new Date().getTime();
System.out.println("Set end time:"+ endTime1);
System.out.println("result of set:" + (endTime1 - startTime1));
System.out.println("number of Set:" + resultSet.size() + "\n");
long startTime2 = new Date().getTime();
System.out.println("Map start time:" + startTime1);
Map<Integer, Integer> resultMap = new HashMap<Integer, Integer>();
for (int i = 0; i < input.length; i++) {
if (!resultMap.containsKey(input[i]))
resultMap.put(input[i], input[i]);
}
long endTime2 = new Date().getTime();
System.out.println("Map end Time:" + endTime2);
System.out.println("result of Map:" + (endTime2 - startTime2));
System.out.println("number of Map:" + resultMap.size());
Here is result:
Set start time:1441960583837
Set end time:1441960583917
result of set:80
number of Set:198652
Map start time:1441960583837
Map end Time:1441960583983
result of Map:66
number of Map:198652

This is not using Set, Map, List or any extra collection, only two arrays:
package arrays.duplicates;
import java.lang.reflect.Array;
import java.util.Arrays;
public class ArrayDuplicatesRemover<T> {
public static <T> T[] removeDuplicates(T[] input, Class<T> clazz) {
T[] output = (T[]) Array.newInstance(clazz, 0);
for (T t : input) {
if (!inArray(t, output)) {
output = Arrays.copyOf(output, output.length + 1);
output[output.length - 1] = t;
}
}
return output;
}
private static <T> boolean inArray(T search, T[] array) {
for (T element : array) {
if (element.equals(search)) {
return true;
}
}
return false;
}
}
And the main to test it
package arrays.duplicates;
import java.util.Arrays;
public class TestArrayDuplicates {
public static void main(String[] args) {
Integer[] array = {1, 1, 2, 2, 3, 3, 3, 3, 4};
testArrayDuplicatesRemover(array);
}
private static void testArrayDuplicatesRemover(Integer[] array) {
final Integer[] expectedResult = {1, 2, 3, 4};
Integer[] arrayWithoutDuplicates = ArrayDuplicatesRemover.removeDuplicates(array, Integer.class);
System.out.println("Array without duplicates is supposed to be: " + Arrays.toString(expectedResult));
System.out.println("Array without duplicates currently is: " + Arrays.toString(arrayWithoutDuplicates));
System.out.println("Is test passed ok?: " + (Arrays.equals(arrayWithoutDuplicates, expectedResult) ? "YES" : "NO"));
}
}
And the output:
Array without duplicates is supposed to be: [1, 2, 3, 4]
Array without duplicates currently is: [1, 2, 3, 4]
Is test passed ok?: YES