I want my program to randomly generate 1 and 0 but it should look like it's in a queue. The 1 is represented by a person and 0 means that there's no person. It should generate random 1 and 0 like this 0 0 0 0 1 1 1 1 1 1, if the line is in the left and vice versa if it's in the right, not like this 1 1 1 0 0 1 0 0 1 1.
public void randPeople(){
int person1 = rand.nextInt((1 - 0) + 1) + 0;
int person2 = rand.nextInt((1 - 0) + 1) + 0;
int person3 = rand.nextInt((1 - 0) + 1) + 0;
int person4 = rand.nextInt((1 - 0) + 1) + 0;
int person5 = rand.nextInt((1 - 0) + 1) + 0;
int person6 = rand.nextInt((1 - 0) + 1) + 0;
int person7 = rand.nextInt((1 - 0) + 1) + 0;
int person8 = rand.nextInt((1 - 0) + 1) + 0;
int person9 = rand.nextInt((1 - 0) + 1) + 0;
int person10 = rand.nextInt((1 - 0) + 1) + 0;
EntryFloor1.setText(Integer.toString(person1) + " " + Integer.toString(person2) + " " +
Integer.toString(person3) + " " + Integer.toString(person4) + " " +
Integer.toString(person5) + " " + Integer.toString(person6) + " " +
Integer.toString(person7) + " " + Integer.toString(person8) + " " +
Integer.toString(person9) + " " + Integer.toString(person10));
}
Implemented a simple random function to generate 0s and 1s
int[] queue = new int[10];
Random r = new Random();
int rand = r.nextInt(queue.length);
int r1 = 1 - rand % 2;
int r2 = rand % 2;
for (int i = 0; i < queue.length; i++) {
if (i <= rand) {
queue[i] = r1;
} else {
queue[i] = r2;
}
}
System.out.println("Queue " + Arrays.toString(queue));
output
Queue [1, 1, 1, 0, 0, 0, 0, 0, 0, 0]
With Java8 generator
final int size = 10;
final Random random = new Random();
boolean order = random.nextBoolean();
Object[] arr = IntStream.generate(() -> random.nextInt(size) % 2).limit(size).boxed().sorted((i1, i2) -> order ? i1 - i2 : i2 - i1).toArray();
System.out.println("Arrays " + Arrays.toString(arr));
output
Arrays [1, 1, 1, 1, 1, 0, 0, 0, 0, 0]
I believe this will do what you want. Just as a side note - if you only care about whether or not a person exists I would suggest using boolean values to represent the people. Since you specifically said 1 and 0 I wrote the code below to produce that output. You'll notice that I do use the nextBoolean() method of the Random class as it is simpler and more readable for what I'm doing.
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class RandPeopleMain {
public static void main(String[] args) {
System.out.println(lineUpLeft(10));
System.out.println(lineUpRight(10));
}
public static List<Integer> lineUpLeft(int numPeople){
Random rand = new Random();
List<Integer> list = new ArrayList<Integer>();
for(int i=0; i < numPeople; i++){
boolean person = rand.nextBoolean();
if(person){
list.add(1);
}
}
for(int i=list.size(); i < numPeople; i++){
list.add(0);
}
return list;
}
public static List<Integer> lineUpRight(int numPeople){
Random rand = new Random();
List<Integer> list = new ArrayList<Integer>();
for(int i=0; i < numPeople; i++){
boolean person = rand.nextBoolean();
if(person){
list.add(1);
}
}
for(int i=list.size(); i < numPeople; i++){
list.add(0, 0);
}
return list;
}
}
Example output:
[1, 1, 1, 1, 1, 1, 0, 0, 0, 0]
[0, 0, 0, 1, 1, 1, 1, 1, 1, 1]
I provided the above methods to illustrate how similar aligning the people left or right can be. Here is a more generic version that uses a single method with an additional parameter to specify the alignment.
public static List<Integer> lineUpPeople(int numPeople, boolean alignLeft){
Random rand = new Random();
List<Integer> list = new ArrayList<Integer>();
for(int i=0; i < numPeople; i++){
boolean person = rand.nextBoolean();
if(person){
list.add(1);
}
}
for(int i=list.size(); i < numPeople; i++){
if(alignLeft)
list.add(0);
else
list.add(0,0);
}
return list;
}
Lastly, here is another way to approach the problem. Rather than generating a random value for each potential person simply generate the number of people and then fill in the list/queue appropriately.
public static List<Integer> lineUp(int maxPeople, boolean alignLeft){
Random rand = new Random();
int numPeople = rand.nextInt(maxPeople+1);
List<Integer> list = new ArrayList<Integer>();
for(int i=0; i < maxPeople; i++){
if(i < numPeople)
list.add(1);
else if(alignLeft)
list.add(0);
else
list.add(0,0);
}
return list;
}
Try this:
Random r = new Random();
boolean b = r.nextBoolean(); // left or right
int l = r.nextInt(11); // breakpoint to change from 0 to 1 or other way
System.out.println(b + " " + l);
int person[] = new int[10];
for (int i = 0; i < 10; i++) {
if (b) {
if (i < l)
person[i] = 1;
else
person[i] = 0;
} else {
if (i < l)
person[i] = 0;
else
person[i] = 1;
}
}
System.out.println(Arrays.toString(person));
Related
So in my advanced algorithms class, we are to write an algorithm for a program to find two numbers in two sorted arrays of integers. The format is A[i] + B[j] == x. The runtime of the algorithm needs to be O(n).
I thought i had it and wanted to check so I emailed my professor and she told me my runtime was O(n^2). Here is my code:
int[] A = {1,2,3,4,5};
int[] B = {1,2,3,4,5,6};
int x = 4;
int i = 0;
int j = 0;
for(int n = 0; n < (A.length*B.length); n++) {
if(i >= A.length)
i = 0;
if(n % B.length == 0)
j++;
if(A[i] + B[j] == x) {
System.out.println(A[i] + " + " + B[j] + " = " + x);
break;
}
i++;
}
EDIT
I do apologize if this is still incorrect. I never really grasped the concept of Big-Oh. Would this change the runtime to O(n)? I got rid of the A.length*B.length and tried something a little different.
int[] A = {1,2,3,4,5};
int[] B = {1,2,3,4,5};
int x = 5;
int i = 0;
int j = 0;
while(i < A.length) {
if(B[j] == x - A[i]) {
/* exit */ }
if(j >= B.length) {
j = 0;
i++; }
j++;
}
Solution 1:
Add all values in B to a Map with B value as the map key, and B-index as the map value.
Iterate A, and calculate desired B value as B = x - A. Look for it in the map, and if found, you then have the index.
You will only iterate A and B once each. Adding a single value to map is O(1), and looking up a value is O(1), assuming a HashMap, so overall is O(n).
Solution 2:
Iterate A ascending, and B descending.
For each value in A, look at current B value. Walk down B until A + B <= x (or you reach beginning of B).
You will only iterate A and B once each, so O(n).
Solution 2 requires less memory (no map), and is likely faster (no time spent building map).
UPDATE Here is code:
The above descriptions were based on need for index of values, and the code for each solution is:
Solution 1
private static void findSum(int[] a, int[] b, int x) {
Map<Integer, Integer> bIdx = new HashMap<>();
for (int j = 0; j < b.length; j++)
bIdx.put(b[j], j);
for (int i = 0; i < a.length; i++) {
Integer j = bIdx.get(x - a[i]);
if (j != null)
System.out.println("a[" + i + "] + b[" + j + "] = " + a[i] + " + " + b[j] + " = " + x);
}
}
Solution 2
private static void findSum(int[] a, int[] b, int x) {
for (int i = 0, j = b.length - 1, sum; i < a.length && j >= 0; i++) {
while (j >= 0 && (sum = a[i] + b[j]) >= x) {
if (sum == x)
System.out.println("a[" + i + "] + b[" + j + "] = " + a[i] + " + " + b[j] + " = " + x);
j--;
}
}
}
Test
int[] a = {1,2,3,4,5};
int[] b = {1,2,3,4,5,6};
findSum(a, b, 4);
Output (same from both)
a[0] + b[2] = 1 + 3 = 4
a[1] + b[1] = 2 + 2 = 4
a[2] + b[0] = 3 + 1 = 4
Solution 1 using Set
If you don't need index position, then a Set is better for solution 1:
private static void findSum(int[] aArr, int[] bArr, int x) {
Set<Integer> bSet = new HashSet<>();
for (int b : bArr)
bSet.add(b);
for (int a : aArr)
if (bSet.contains(x - a))
System.out.println(a + " + " + (x - a) + " = " + x);
}
Output
1 + 3 = 4
2 + 2 = 4
3 + 1 = 4
Here is an example of how you can measure your time, i've included another method to find the numbers you mentioned. See the difference in runtime:
int[] A = {1,2,3,4,5};
int[] B = {1,2,3,4,5,6};
int x = 4;
int i = 0;
int j = 0;
long t1 = System.nanoTime();
for(int n = 0; n < (A.length*B.length); n++) {
if(i >= A.length)
i = 0;
if(n % B.length == 0)
j++;
if(A[i] + B[j] == x) {
System.out.println(A[i] + " + " + B[j] + " = " + x);
break;
}
i++;
}
long t2 = System.nanoTime();
System.out.println("Time 1: "+(t2-t1));
//Here's the other method
long t3 = System.nanoTime();
for (int n = 0;n<B.length;n++){
for (int m =0;m<A.length;m++){
if(A[m]+B[n]==x){
System.out.println(A[m] +" + "+B[n] +" = "+ x);
}
}
}
long t4 = System.nanoTime();
System.out.println("Time 2: "+(t4-t3));
Here is the code, for Andreas's Solution 1, that I came up with:
int[] A = {2,3,4};
int[] B = {7,9};
Map<Integer, Integer> hashMap = new HashMap<Integer, Integer>();
int x = 10;
int b;
for(int i = 0; i < B.length; i++) {
hashMap.put(B[i], i);
}
for (int n = 0; n < A.length; n++){
b = x - A[n];
if(hashMap.get(b) != null)
System.out.println(A[n] + " + " + b + " = " + x);
}
I need to design an algorithm to find the maximum value I can get from (stepping) along an int[] at predefined (step lengths).
Input is the number of times we can "use" each step length; and is given by n2, n5 and n10. n2 means that we move 2 spots in the array, n5 means 5 spots and n10 means 10 spots. We can only move forward (from left to right).
The int[] contains the values 1..5, the size of the array is (n2*2 + n5*5 + n10*10). The starting point is int[0].
Example: we start at int[0]. From here we can move to int[0+2] == 3, int[0+5] == 4 or int[0+10] == 1. Let's move to int[5] since it has the highest value. From int[5] we can move to int[5+2], int[5+5] or int[5+10] etc.
We should move along the array in step lengths of 2, 5 or 10 (and we can only use each step length n2-, n5- and n10-times) in such a manner that we step in the array to collect as high sum as possible.
The output is the maximum value possible.
public class Main {
private static int n2 = 5;
private static int n5 = 3;
private static int n10 = 2;
private static final int[] pokestops = new int[n2 * 2 + n5 * 5 + n10 * 10];
public static void main(String[] args) {
Random rand = new Random();
for (int i = 0; i < pokestops.length; i++) {
pokestops[i] = Math.abs(rand.nextInt() % 5) + 1;
}
System.out.println(Arrays.toString(pokestops));
//TODO: return the maximum value possible
}
}
This is an answer in pseudocode (I didn't run it, but it should work).
fill dp with -1.
dp(int id, int 2stepcount, int 5stepcount, int 10stepcount) {
if(id > array_length - 1) return 0;
if(dp[id][2stepcount][5stepcount][10stepcount] != -1) return dp[id][2stepcount][5stepcount][10stepcount];
else dp[id][2stepcount][5stepcount][10stepcount] = 0;
int 2step = 2stepcount < max2stepcount? dp(id + 2, 2stepcount + 1, 5stepcount, 10stepcount) : 0;
int 5step = 5stepcount < max5stepcount? dp(id + 5, 2stepcount, 5stepcount + 1, 10stepcount) : 0;
int 10step = 10stepcount < max10stepcount? dp(id + 10, 2stepcount, 5stepcount, 10stepcount + 1) : 0;
dp[id][2stepcount][5stepcount][10stepcount] += array[id] + max(2step, 5step, 10step);
return dp[id][2stepcount][5stepcount][10stepcount];
}
Call dp(0,0,0,0) and the answer is in dp[0][0][0][0].
If you wanna go backwards, then you do this:
fill dp with -1.
dp(int id, int 2stepcount, int 5stepcount, int 10stepcount) {
if(id > array_length - 1 || id < 0) return 0;
if(dp[id][2stepcount][5stepcount][10stepcount] != -1) return dp[id][2stepcount][5stepcount][10stepcount];
else dp[id][2stepcount][5stepcount][10stepcount] = 0;
int 2stepForward = 2stepcount < max2stepcount? dp(id + 2, 2stepcount + 1, 5stepcount, 10stepcount) : 0;
int 5stepForward = 5stepcount < max5stepcount? dp(id + 5, 2stepcount, 5stepcount + 1, 10stepcount) : 0;
int 10stepForward = 10stepcount < max10stepcount? dp(id + 10, 2stepcount, 5stepcount, 10stepcount + 1) : 0;
int 2stepBackward = 2stepcount < max2stepcount? dp(id - 2, 2stepcount + 1, 5stepcount, 10stepcount) : 0;
int 5stepBackward = 5stepcount < max5stepcount? dp(id - 5, 2stepcount, 5stepcount + 1, 10stepcount) : 0;
int 10stepBackward = 10stepcount < max10stepcount? dp(id - 10, 2stepcount, 5stepcount, 10stepcount + 1) : 0;
dp[id][2stepcount][5stepcount][10stepcount] += array[id] + max(2stepForward, 5stepForward, 10stepForward, 2stepBackward, 5backForward, 10backForward);
return dp[id][2stepcount][5stepcount][10stepcount];
}
But your paths don't get fulled explored, because we stop if the index is negative or greater than the array size - 1, you can add the wrap around functionality, I guess.
this is a solution but i am not sure how optimal it is !
i did some optimization on it but i think much more can be done
I posted it with the example written in question
import java.util.Arrays;
import java.util.Random;
public class FindMax {
private static int n2 = 5;
private static int n5 = 3;
private static int n10 = 2;
private static final int[] pokestops = new int[n2 * 2 + n5 * 5 + n10 * 10];
public static int findMaxValue(int n2, int n5, int n10, int pos, int[] pokestops) {
System.out.print("|");
if (n2 <= 0 || n5 <= 0 || n10 <= 0) {
return 0;
}
int first;
int second;
int third;
if (pokestops[pos] == 5 || ((first = findMaxValue(n2 - 1, n5, n10, pos + 2, pokestops)) == 5) || ((second = findMaxValue(n2, n5 - 1, n10, pos + 5, pokestops)) == 5) || ((third = findMaxValue(n2, n5, n10 - 1, pos + 10, pokestops)) == 5)) {
return 5;
}
return Math.max(Math.max(Math.max(first, second), third), pokestops[pos]);
}
public static void main(String[] args) {
Random rand = new Random();
for (int i = 0; i < pokestops.length; i++) {
pokestops[i] = Math.abs(rand.nextInt() % 5) + 1;
}
System.out.println(Arrays.toString(pokestops));
//TODO: return the maximum value possible
int max = findMaxValue(n2, n5, n10, 0, pokestops);
System.out.println("");
System.out.println("Max is :" + max);
}
}
You need to calculate following dynamic programming dp[c2][c5][c10][id] - where c2 is number of times you've stepped by 2, c5 - by 5, c10 - by 10 and id - where is your current position. I will write example for c2 and c5 only, it can be easily extended.
int[][][][] dp = new int[n2 + 1][n5 + 1][pokestops.length + 1];
for (int[][][] dp2 : dp) for (int[][] dp3 : dp2) Arrays.fill(dp3, Integer.MAX_VALUE);
dp[0][0][0] = pokestops[0];
for (int c2 = 0; c2 <= n2; c2++) {
for (int c5 = 0; c5 <= n5; c5++) {
for (int i = 0; i < pokestops.length; i++) {
if (c2 < n2 && dp[c2 + 1][c5][i + 2] < dp[c2][c5][i] + pokestops[i + 2]) {
dp[c2 + 1][c5][i + 2] = dp[c2][c5][i] + pokestops[i + 2];
}
if (c5 < n5 && dp[c2][c5 + 1][i + 5] < dp[c2][c5][i] + pokestops[i + 5]) {
dp[c2][c5 + 1][i + 5] = dp[c2][c5][i] + pokestops[i + 5];
}
}
}
}
I know the target language is java, but I like pyhton and conversion will not be complicated.
You can define a 4-dimensional array dp where dp[i][a][b][c] is the maximum value that you can
get starting in position i when you already has a steps of length 2, b of length 5 and c of length
10. I use memoization to get a cleaner code.
import random
values = []
memo = {}
def dp(pos, n2, n5, n10):
state = (pos, n2, n5, n10)
if state in memo:
return memo[state]
res = values[pos]
if pos + 2 < len(values) and n2 > 0:
res = max(res, values[pos] + dp(pos + 2, n2 - 1, n5, n10))
if pos + 5 < len(values) and n5 > 0:
res = max(res, values[pos] + dp(pos + 5, n2, n5 - 1, n10))
if pos + 10 < len(values) and n10 > 0:
res = max(res, values[pos] + dp(pos + 10, n2, n5, n10 - 1))
memo[state] = res
return res
n2, n5, n10 = 5, 3, 2
values = [random.randint(1, 5) for _ in range(n2*2 + n5*5 + n10*10)]
print dp(0, n2, n5, n10)
Suspiciously like homework. Not tested:
import java.util.Arrays;
import java.util.Random;
public class Main {
private static Step[] steps = new Step[]{
new Step(2, 5),
new Step(5, 3),
new Step(10, 2)
};
private static final int[] pokestops = new int[calcLength(steps)];
private static int calcLength(Step[] steps) {
int total = 0;
for (Step step : steps) {
total += step.maxCount * step.size;
}
return total;
}
public static void main(String[] args) {
Random rand = new Random();
for (int i = 0; i < pokestops.length; i++) {
pokestops[i] = Math.abs(rand.nextInt() % 5) + 1;
}
System.out.println(Arrays.toString(pokestops));
int[] initialCounts = new int[steps.length];
for (int i = 0; i < steps.length; i++) {
initialCounts[i] = steps[i].maxCount;
}
Counts counts = new Counts(initialCounts);
Tree base = new Tree(0, null, counts);
System.out.println(Tree.max.currentTotal);
}
static class Tree {
final int pos;
final Tree parent;
private final int currentTotal;
static Tree max = null;
Tree[] children = new Tree[steps.length*2];
public Tree(int pos, Tree parent, Counts counts) {
this.pos = pos;
this.parent = parent;
if (pos < 0 || pos >= pokestops.length || counts.exceeded()) {
currentTotal = -1;
} else {
int tmp = parent == null ? 0 : parent.currentTotal;
this.currentTotal = tmp + pokestops[pos];
if (max == null || max.currentTotal < currentTotal) max = this;
for (int i = 0; i < steps.length; i++) {
children[i] = new Tree(pos + steps[i].size, this, counts.decrement(i));
// uncomment to allow forward-back traversal:
//children[2*i] = new Tree(pos - steps[i].size, this, counts.decrement(i));
}
}
}
}
static class Counts {
int[] counts;
public Counts(int[] counts) {
int[] tmp = new int[counts.length];
System.arraycopy(counts, 0, tmp, 0, counts.length);
this.counts = tmp;
}
public Counts decrement(int i) {
int[] tmp = new int[counts.length];
System.arraycopy(counts, 0, tmp, 0, counts.length);
tmp[i] -= 1;
return new Counts(tmp);
}
public boolean exceeded() {
for (int count : counts) {
if (count < 0) return true;
}
return false;
}
}
static class Step {
int size;
int maxCount;
public Step(int size, int maxCount) {
this.size = size;
this.maxCount = maxCount;
}
}
}
There's a line you can uncomment to allow forward and back movement (I'm sure someone said in the comments that was allowed, but now I see in your post it says forward only...)
I am trying to answer the following question: given a sorted array with some sequenced numbers and some non-sequenced numbers, write an algorithm that obtains a pair {start, end} for each group of consecutive numbers. Consecutive numbers have difference of 1 only.
So far, I can think of the brute force method only:
public static void main(String[] args) {
int[] array = { 4, 5, 6, 7, 8, 9, 12, 15, 16, 17, 18, 20, 22, 23, 24, 27 };
Map<Integer, Integer> list = new HashMap<Integer, Integer>();
list = findIndex(array);
}
// Bruteforce
private static Map<Integer, Integer> findIndex(int[] array) {
Map<Integer, Integer> list = new HashMap<Integer, Integer>();
int x = -1, y = -1;
int end = array.length;
for (int i = 0; i < end; i++) {
x = i;
while (i < end - 1) {
if (array[i] + 1 == array[i + 1]) {
i++;
y = i;
} else {
if (x != y && x >= 0) {
list.put(x, y);
System.out.println("i = " + x + " to j = " + y);
i = i + 1;
break;
}
}
}
}
return list;
}
Output :
i = 0 to j = 5
i = 7 to j = 10
i = 12 to j = 14
It works fine, but how do I improve time complexity?
You don't need to nest loops for this:
int end = array.length;
if (end > 0) {
int start = 0;
for (int i = 1; i < end; i++) {
if (array[i] != array[i - 1] + 1) {
if (i - start > 1) {
list.put(start, i - 1);
System.out.println("i = " + start + " to j = " + (i - 1));
}
start = i;
}
}
if (end - start > 1) {
list.put(start, end - 1);
System.out.println("i = " + start + " to j = " + (end - 1));
}
}
As soon as initial array sorted, you can have O(N) implementation of this algorithm like this:
private static Map<Integer, Integer> getConsecutive(final int[] array) {
final Map<Integer, Integer> list = new TreeMap<Integer, Integer>();
int startIndex = 0;
int endIndex = 0;
for (int i = 1; i < array.length; i++) {
if (array[i - 1] + 1 == array[i])
endIndex = i;
else {
if (endIndex > startIndex)
list.put(startIndex, endIndex);
startIndex = endIndex = i;
}
}
if (endIndex > startIndex)
list.put(startIndex, endIndex);
return list;
}
I'm trying to make the merge sort to use only (n/2 + 1) extra space and still O(n log n) time. This is my homework.
The original quesetion:
Write the non-recursive version of merge sort. Your program should run
in O(n log n) time and use n/2 + O(1) extra spaces.
The program will split an array in to two like normal merge sort. The left part will be in another array, which is ceil(n/2) long, so it will fit the requirement.
The right part will be in the original array. So it will be half in-place sorting
Sorry, I don't know how to explain further.
I think this is basically correct. But I kept on facing OutOfBounds error.
I know the code is quite long and messy. But can anyone help me about that?
I spent about 5 hours to implement this. Please help me.
package comp2011.lec6;
import java.util.Arrays;
public class MergeSort {
public static void printArr(int[] arr){
for(int i = 0; i < arr.length; i++){
System.out.printf("%d ", arr[i]);
}
}
public static void mergeSort(int[] arr){
if(arr.length<2) {
return;
}
int n, lBegin, rBegin;
n = 1;
int[] leftArr = new int[arr.length - (arr.length/2)];
while(n<arr.length) {
lBegin = 0;
rBegin = n;
while(rBegin + n <= arr.length) {
mergeArrays(arr, lBegin, lBegin+n, rBegin, rBegin+n, leftArr);
lBegin = rBegin+n;
rBegin = lBegin+n;
}
if(rBegin < arr.length) {
mergeArrays(arr, lBegin, lBegin+n, rBegin, arr.length, leftArr);
}
n = n*2;
}
}
public static void mergeArrays(int[] array, int startL, int stopL, int startR, int stopR, int[] leftArr) {
// int[] right = new int[stopR - startR + 1];
// int[] left = new int[stopL - startL + 1];
// for(int i = 0, k = startR; i < (right.length - 1); ++i, ++k) {
// right[i] = array[k];
// }
System.out.println("==============");
System.out.println("stopL: " + stopL +" startL: " + startL);
for(int i = 0, k = startL; i <= (stopL - startL); ++i, ++k) {
System.out.println(leftArr[i]);
leftArr[i] = array[k];
}
// right[right.length-1] = Integer.MAX_VALUE;
leftArr[stopL - startL] = Integer.MAX_VALUE;
System.out.println("leftArr: " + Arrays.toString(leftArr));
System.out.println("RightArr: " + Arrays.toString(Arrays.copyOfRange(array, startR, stopR)));
System.out.println("before: " + Arrays.toString(array));
// for(int k = startL, m = 0, n = startR; k < stopR; ++k) {
System.out.println("StartL: " + startL + " StartR: " + stopR);
for(int k = startL, m = 0, n = startR; ( (k < stopR) ); ++k) {
System.out.println("k: " + k);
System.out.println("Left: " + leftArr[m]);
System.out.println("Right: " + array[n]);
System.out.println("Array[k] before: " + array[k]);
// if(leftArr[m] == Integer.MAX_VALUE){
// System.out.println("YES");
// }
if( (leftArr[m] <= array[n]) || (n >= stopR) ) {
System.out.println("Left is smaller than right");
array[k] = leftArr[m];
m++;
}
else {
System.out.println("Right is smaller than left");
array[k] = array[n];
System.out.println("right: " + array[k]);
n++;
}
System.out.println("Array[k] after: " + array[k]+"\n");
}
System.out.println("after " + Arrays.toString(array));
}
public static void main(String[] args) {
int[] array = new int[] { 5, 2, 4, 12, 2, 10, 13, 1, 7 };
mergeSort(array);
printArr(array);
}
}
I have some code that will brute force solve the following problem:
Given a set of x coins and a target sum to reach, what is the fewest number of coins required to reach that target?
The code so far:
import java.util.ArrayList;
import java.util.Arrays;
public class coinsSum {
public static int min = Integer.MAX_VALUE;
public static int[] combination;
public static final int TARGET = 59;
public static void main(String[] args) {
long start = System.nanoTime();
int[] validCoins = new int[] {1, 2, 5, 10, 20};
Arrays.sort(validCoins);
int len = validCoins.length;
ArrayList<Integer> maxList = new ArrayList<Integer>();
for(int c : validCoins) {
maxList.add(TARGET / c);
}
int[] max = new int[len];
for(int i = 0; i < len; i++) {
max[i] = maxList.get(i).intValue();
}
permutations(new int[len], max, validCoins, 0); // bread&butter
if(min != Integer.MAX_VALUE) {
System.out.println();
System.out.println("The combination " + Arrays.toString(combination) + " uses " + min + " coins to make the target of: " + TARGET);
} else {
System.out.println("The target was not reachable using these coins");
}
System.out.println("TOOK: " + (System.nanoTime() - start) / 1000000 + "ms");
}
public static void permutations(int[] workspace, int[] choices, int[] coins, int pos) {
if(pos == workspace.length) {
int sum = 0, coinCount = 0;
System.out.println("TRYING " + Arrays.toString(workspace));
for(int a = 0; a < coins.length; a++) {
sum += workspace[a] * coins[a];
coinCount += workspace[a];
}
if(sum == TARGET) {
// System.out.println(Arrays.toString(n)); //valid combinations
if(coinCount < min) {
min = coinCount;
combination = workspace;
System.out.println(Arrays.toString(combination)+" uses " + min + " coins");
}
}
return;
}
for(int i = 0; i <= choices[pos]; i++) {
workspace[pos] = i;
permutations(workspace, choices, coins, pos + 1);
}
}
}
This solution uses recursion, is there any way to do compute combinations in java using loops?
How else can all possible combinations be iterated through?
You can sort the array of coins. Then go from right to left, keep subtracting from the target value, untill the coin is bigger from the remaining value of target. Move left in the array of coins and repeat the process.
Example:
{1, 2, 5, 10, 20}
num = 59
Try coins from right to left:
59 - 20 = 39
So far coins used [20]
39 - 20 = 19
So far coins used [20,20]
19 - 20 = -1, Can't use 20!
19 - 10 = 9
So far coins used [20,20,10]
9 - 10 = -1, Can't use 10!
9 - 5 = 4
So far coins used [20,20,10,5]
4 - 5 = -1, Can't use 5!
4 - 2 = 2
So far coins used [20,20,10,5,2]
2 - 2 = 0
So far coins used [20,20,10,5,2,2]
Total coin used 6
Here is a solution in python that uses dynamic programming to find the minimum number of coins to reach a target value.
The algorithm works as follow
dp[i][target] = minimum number of coins required required to acheive target using first i coin
dp[i][target] = min(dp[i-1][target],dp[i-1][target-coin[i]]+1)
dp[i-1][target] denotes not using the ith coin
dp[i-1][target-coin[i]] denotes making use of ith coin
Since for each coin your are checking wheather to include it or not the algorithm is enumerating through all possible combination.
Here is an space optimized version of the above algorithm
maxvalue = 10 ** 9
def minchange(coins, target):
no_of_coins = len(coins)
dp = [maxvalue for i in range(target + 1) ]
dp[0] = 0
for i in range(no_of_coins):
for j in range(coins[i], target + 1):
dp[j] = min(dp[j], dp[j - coins[i]] + 1)
return dp[target]
I found a dynamic programming approach which is definitely not optimised, but isn't too bad for target numbers up to 10000 if anyone is interested
import java.util.*;
public class coinSumMinimalistic {
public static final int TARGET = 12003;
public static int[] validCoins = {1, 3, 5, 6, 7, 10, 12};
public static void main(String[] args) {
Arrays.sort(validCoins);
sack();
}
public static void sack() {
Map<Integer, Integer> coins = new TreeMap<Integer, Integer>();
coins.put(0, 0);
int a = 0;
for(int i = 1; i <= TARGET; i++) {
if(a < validCoins.length && i == validCoins[a]) {
coins.put(i, 1);
a++;
} else coins.put(i, -1);
}
for(int x = 2; x <= TARGET; x++) {
if(x % 5000 == 0) System.out.println("AT: " + x);
ArrayList<Integer> list = new ArrayList<Integer>();
for(int i = 0; i <= x / 2; i++) {
int j = x - i;
list.add(i);
list.add(j);
}
coins.put(x, min(list, coins));
}
System.out.println("It takes " + coins.get(TARGET) + " coins to reach the target of " + TARGET);
}
public static int min(ArrayList<Integer> combos, Map<Integer, Integer> coins) {
int min = Integer.MAX_VALUE;
int total = 0;
for(int i = 0; i < combos.size() - 1; i += 2) {
int x = coins.get(combos.get(i));
int y = coins.get(combos.get(i + 1));
if(x < 0 || y < 0) continue;
else {
total = x + y;
if(total > 0 && total < min) {
min = total;
}
}
}
int t = (min == Integer.MAX_VALUE || min < 0) ? -1:min;
return t;
}
public static void print(Map<Integer, Integer> map) {
for(Map.Entry<Integer, Integer> entry : map.entrySet()) {
System.out.println("[" + entry.getKey() + ", " + entry.getValue() + "]");
}
System.out.println();
}
}