We Keep Coding

Java finding the smallest integer in a speciofic position in a sets of integer

Algorithm:
Procedure SELECT( k,S)
{ if ISI =1 then return the single element in S
else { choose an element a randomly from S;
let S1,S2,and S3 be he sequences of elements in S
less than, equal to, and greater than m, respectively;
if IS1I >=k then return SELECT(k,S1)
else
if (IS1I + IS2I >=k then return m
else return SELECT(k-IS1I-IS2I , S3);
}
}
The question is to implement the first algorithm for finding the kth smallest integer in a set of integers and test your program for different sets of integers generated by a random number generator.
Below is my solution.
import java.util.Random;
import java.util.Scanner;
public class main {
private static Random rand = new Random();
private static Scanner keyboard = new Scanner(System.in);
public static int firstAlgorithm(int k, int[] S) {
int m = S[rand.nextInt(S.length)];
int[] S1 = new int[S.length];
int[] S2 = new int[S.length];
int[] S3 = new int[S.length];
int p = 0;
int q = 0;
int r = 0;
if (S.length == 1)
return S[0];
for (int i = 0; i < S.length; i++) {
if (S[i] < m) {
S1[p] = S[i];
p++;
} else if (S[i] == m) {
S2[q] = S[i];
q++;
} else {
S3[r] = S[i];
r++;
}
}
S1 = trimToSize(S1, p);
S2 = trimToSize(S2, q);
S3 = trimToSize(S3, r);
if (S1.length >= k)
return firstAlgorithm(k, S1);
else if (S1.length + S2.length >= k)
return m;
else
return firstAlgorithm(k - S1.length - S2.length, S3);
}
private static int[] trimToSize(int[] arr, int size) {
int[] temp = new int[size];
for (int i = 0; i < size; i++) {
temp[i] = arr[i];
}
return temp;
}
public static void printArray(int[] S) {
for (int i = 0; i < S.length; i++) {
System.out.print(S[i] + "\t");
if (i % 10 == 9)
System.out.println();
}
}
// start main method
public static void main(String[] args) {
System.out.print("Enter the size of an array: ");
int size = keyboard.nextInt();
while (size < 1) {
System.out.println("Size of the array should be greater than 0.");
System.out.print("Enter the size of an array: ");
size = keyboard.nextInt();
}
System.out.print("Enter the value of k: ");
int k = keyboard.nextInt();
while (k < 1 || k > size) {
System.out.println("Value of k should be in the range 1-" + size + ".");
System.out.print("Enter the value of k: ");
k = keyboard.nextInt();
}
int[] S = new int[size];
for (int i = 0; i < size; i++) {
S[i] = 100 + rand.nextInt(900);
}
System.out.println("\nRandom values generated in the array:");
printArray(S);
System.out.println();
System.out.println(k + "th smallest value in the array using Algorithm #1: " + firstAlgorithm(k, S));
}
}
But I need to implement the above algorithm without using a temporary array for partitioning. How can I do it?

The algorithm is Dijkstra's 3-way partition.
You will have to modify the original S.
Untested (pseudo) code ahead
public static int partition(int left, int right, int[] S) {
int m = rand.nextInt(right-left); // protect against malicious data
swap(S[left+m], S[right]);
int equal = left;
while (left < right) {
if (a[left] < a[n])
swap(S, left++, equal++)
else if (a[left] == a[n])
swap(S, left, --right);
else
left++;
}
return left, equal;
}
public static int firstAlgorithm(int k, int left, int right, int[] S) {
if (left == right)
return S[left];
int p, e = partition(left, right, S); // returns 2 values. S1=[0,p), S2=[p,e), S3=[e, n)
if (p >= k)
return firstAlgorithm(k, left, p, S);
else if (e >= k) // p < k
return S[p]; // p is the first equal, e is first larger than equal
else // e < k
return firstAlgorithm(k, e, right, S);
}
// test
S = {1, 4, 2, 6, 2};
k = 2;
int result = firstAlgorithm(2, 0, S.length-1, S);
assert(result == 2);
Warning syntax and off-by-one errors guarantied.
See here multiple ways to return 2 values in java.

Coding Heapsort Algorithm but am getting a Stack Overflow error and cannot figure out why

Below is my code, I keep getting a Stack Overflow error from the last statement in my code which is the recursive call for heapify (the max heapify) method. Please help.
Class 1 code
package hw3javasorttest;
import java.util.*;
public class HW3JavaSortTest {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
System.out.println("Unsorted array");
System.out.print("[");
int[] arr = new int[30];
for(int i = 0; i < arr.length; i++) {
arr[i] = (int)(Math.random() * 100);
System.out.print(arr[i] + " ");
}
System.out.println("]");
Scanner in = new Scanner(System.in);
System.out.println("Please enter one of the corresponding numbers to choose the sorting method: ");
System.out.print("1.Heap Sort\n2.Quick Sort");
int Sorting = in.nextInt();
int x;
int q;
x = arr[0];
q = arr[29];
switch (Sorting) {
case 1: System.out.println("Heap Sort:");
HW3JavaSort.HeapSort(arr);
System.out.println(Arrays.toString(arr));
break;
case 2: System.out.println("Quick Sort:");
System.out.println();
// HW3JavaSort.quickSort(arr, x, q);
// System.out.println(Arrays.toString(a));
break;
default: System.out.println("invalid entry");
break;
}
}
}
Class 2 code
package hw3javasorttest;
public class HW3JavaSort {
public static void printArr(int[] arr) { //Method that displays arr
System.out.print("[");
for(int i= 0; i<arr.length; i++){
if(i==arr.length-1) {
System.out.printf("%d]\n", arr[i]);
}
else {
System.out.printf("%d,", arr[i]);
}
}
}
public static void HeapSort(int[] arr) {
int Length = arr.length;
int placeholder;
BuildMaxHeap(arr, Length);
for(int i = arr.length-1; i>0; i--) {
placeholder = arr[0];
arr[0] = arr[i];
arr[i] = placeholder;
heapify(arr, 1, i);
}
}
public static void BuildMaxHeap(int[] arr, int n){ //Organizes max heap
if(arr == null) {
throw new NullPointerException("null");
}
if(arr.length <=0 || n <= 0) {
throw new IllegalArgumentException("illegal");
}
if(n > arr.length) {
n = arr.length;
}
for(int i = n/2; i>= 0; i--) {
heapify(arr, i, n);
}
}
public static void heapify(int [] arr, int i, int n) { //Makes max heap
int largest;
int lc = 2*i;
int rc = 2*i + 1;
int temp = 0;
if(lc<=n && arr[lc-1] > arr[i-1]) {
largest = lc;
} else {
largest = i;
}
if(rc<=n && arr[rc-1] > arr[largest-1]) {
largest = rc;
}
if(largest!=i) {
temp = arr[i-1];
arr[i-1] = arr[largest - 1];
arr[largest - 1] = temp;
heapify(arr, largest, n); //HERE IS WHERE THE COMPILER SAYS I AM //GETTING THE ERROR, SAYS STACK OVERFLOW THEN THE HEAPIFY METHOD THEN THIS LINE //# AND DISPLAYS THE ERROR HUNDREDS OF TIMES
}
}
}

Incorrect formatting caused the algorithm to work differently than expected... fixed by formatting like Java (not Python).
Please take a look at this: https://blog.takipi.com/tabs-vs-spaces-how-they-write-java-in-google-twitter-mozilla-and-pied-piper/

My program seems to be written perfectly, but stops running and allows user input with no scanner?

first time post here.
I am trying to create a class which compares quick sort, merge sort, bubble sort, and selection sort. I have implemented all of the sort methods and created a random array method which populates a random array with 1000 random ints. However when I run my program my main method stops after the initial welcome message and allows for user input. Any help would be greatly appreciated, I'm sure its some simple mistake I am missing.
import java.util.Random;
public class TestSort {
private static int selectCount;
private static int bubbleCount;
private static int mergeCount;
private static int quickCount;
public static void main(String[] args){
System.out.println("Welcome to the search tester. "
+ "We are going to see which algorithm performs the best out of 20 tests");
int testSelection = 0;
int testBubble = 0;
int testQuick = 0;
int testMerge = 0;
//Check tests
int[] a = new int[1000];
populateArray(a);
int[] select = a;
int[] bubble = a;
int[] quick = a;
int[] merge = a;
testSelection = selectionSort(select);
testBubble = bubbleSort(bubble);
testQuick = quickSort(quick,0,0);
testMerge = mergeSort(merge);
System.out.println("Selection sort number of checks: " + testSelection);
System.out.println("Bubble sort number of checks: " + testBubble);
System.out.println("Quick sort number of checks: " + testQuick);
System.out.println("Merge sort number of checks: " + testMerge);
System.out.println("");
}
public static int[] populateArray(int[] a)
{
Random r = new Random();
a = new int[1000];
for(int i=0; i < a.length; i++)
{
int num = r.nextInt(1000);
a[i] = num;
}
return a;
}
//Sorting methods
public static int selectionSort(int[] a)
{
for (int i = 0; i < a.length; i++)
{
int smallestIndex = i;
for (int j=i; j<a.length; j++)
{
if(a[j]<a[smallestIndex])
{
smallestIndex = j;
}
}
if(smallestIndex != i) //Swap
{
int temp = a[i];
a[i] = a[smallestIndex];
a[smallestIndex] = temp;
selectCount++;
}
}
return selectCount;
}
public static int bubbleSort (int[] a)
{
boolean hasSwapped = true;
while (hasSwapped == true)
{
hasSwapped = true;
for(int i = 0; i<a.length-1; i++)
{
if(a[i] > a[i+1]) //Needs to swap
{
int temp = a[i];
a[i] = a[i+1];
a[i+1] = temp;
hasSwapped = true;
bubbleCount++;
}
}
}
return bubbleCount;
}
public static int mergeSort(int [] a)
{
int size = a.length;
if(size<2)//recursive halting point
{
return 0;
}
int mid = size/2;
int leftSize = mid;
int rightSize = size-mid;
int [] left = new int[leftSize];
int [] right = new int[rightSize];
for(int i = 0; i<mid; i++)
{
mergeCount++;
left[i] = a[i];
}
for(int i = mid; i<size; i++)
{
mergeCount++;
right[i-mid]=a[i];
}
mergeSort(left);
mergeSort(right);
//merge
merge(left,right,a);
return mergeCount;
}
private static void merge(int [] left, int [] right, int [] a)
{
int leftSize = left.length;
int rightSize = right.length;
int i = 0;//index of the left array
int j = 0; //index of right array
int k = 0; //index of the sorted array [a]
while(i<leftSize && j<rightSize)
{
if(left[i]<=right[j])
{
a[k] = left[i];
i++;
k++;
}
else
{
a[k] = right[j];
j++;
k++;
}
}
while(i<leftSize)
{
a[k] =left[i];
i++;
k++;
}
while(j<rightSize)
{
a[k] =right[j];
j++;
k++;
}
}
public static int quickSort(int[] a, int left, int right)
{
//partition, where pivot is picked
int index = partition(a,left,right);
if(left<index-1)//Still elements on left to be sorted
quickSort(a,left,index-1);
if(index<right) //Still elements on right to be sorted
quickSort(a,index+1,right);
quickCount++;
return quickCount;
}
private static int partition(int[] a, int left, int right)
{
int i = left;
int j = right; //Left and right are indexes
int pivot = a[(left+right/2)]; //Midpoint, pivot
while(i<j)
{
while(a[i]<pivot)
{
i++;
}
while(a[j]>pivot)
{
j--;
}
if(i<=j) //Swap
{
int temp = a[i];
a[i] = a[j];
a[j] = temp;
i++;
j--;
}
}
return i;
}
}

Your infinite loop is in bubbleSort:
public static int bubbleSort(int[] a)
{
boolean hasSwapped = true;
while (hasSwapped == true)
{
hasSwapped = false; // Need to set this to false
for (int i = 0; i < a.length - 1; i++)
{
if (a[i] > a[i + 1]) // Needs to swap
{
int temp = a[i];
a[i] = a[i + 1];
a[i + 1] = temp;
hasSwapped = true;
bubbleCount++;
}
}
}
return bubbleCount;
}

The problem is in your bubbleSort() method. The hasSwapped boolean is never set to false, so the while loops infinite times.
There is another problem in your code. In the main method, you will have to assign the array that the populateArray() method returns back to a. And the such assignments as int[] select = a; you do in the main method do not do what you want to do. Instead, just send the array a to your sorting methods.
Like this:
int[] a = new int[1000];
a=populateArray(a);
testSelection = selectionSort(a);
testBubble = bubbleSort(a);
testQuick = quickSort(a,0,0);
testMerge = mergeSort(a);

Merge sort 3 way java

I have to make a 3 way merge sort of an array. the array length is a in a power of 3, i.e. 3,9,27 etc. So I can use only one split function and not "left","mid","right".
Would like to get an answer how to repair it and why does not it work.
I have written the code, however don't know how to get it to work.
Here it is:
EDITED THE CODE, STILL DOES NOT WORK
public class Ex3 {
public static void main(String[] args) { //main function
Scanner in = new Scanner(System.in); //scanner
int size = in.nextInt();
int[] arr = new int[size];
for (int i = 0; i<arr.length; i++){
arr[i] = in.nextInt();
}
in.close();
arr = merge3sort (arr); //send to the function to merge
for (int i = 0; i<arr.length; i++){ //printer
System.out.print(arr[i]+ " ");
}
}
static int[] split(int[] m, int thirdNum) { //split function that splits to 3 arrays
int third[] = new int[m.length/3];
int third1[]=new int[m.length/3];
int third2[]=new int[m.length/3];
for(int i = 0; i<=m.length/3; i++)
third[i]=m[i];
for(int i=0; i<=m.length/3;i++)
third1[i]=m[i+thirdNum];
for(int i=0; i<=m.length/3;i++)
third2[i]=m[i+2*thirdNum];
return merge(third,third1,third2);
//return null;
}
static int minOf3(int[] a3) { //function that finds out how what is the index of the smallest number
int num0 = a3[0];
int num1 = a3[1];
int num2 = a3[2];
int idx = 0;
if(num0<num1 && num1<num2)
idx=0;
if(num1<num0 && num0<num2)
idx=1;
else
idx=2;
return idx;
}
static int[] merge(int[] th0, int[] th1, int[] th2) { //function that sorts the numbers between 3 arrays
int len0=th0.length;
int len1=th1.length;
int len2=th2.length;
int[] united = new int[len0+len1+len2];
int ind = 0; int i0=0; int i1=0; int i2=0;
while(i0<len0 && i1<len1 && i2<len2){
if(th0[i0]<th1[i1]){
if(th0[i0]<th2[i2]){
united[ind]=th0[i0];
i0=i0+1;
}//end inner if
else{
united[ind]=th2[i2];
i2=i2+1;
}//end inner else
}//end outer if
else{
united[ind]=th1[i1];
i1=i1+1;
}//end outer else
ind=ind+1;
}//end while
for (int i = i0; i < len0; i = i + 1) {
united[ind] = th0[i];
ind = ind + 1;
}
for (int i = i1; i < len1; i = i + 1) {
united[ind] = th1[i];
ind = ind + 1;
}for (int i = i2; i < len2; i = i + 1) {
united[ind] = th2[i];
ind = ind + 1;
}
return united;
}
static int[] merge3sort(int[] m) { //function that glues all together
if (m.length == 1) {
return m;
}
else{
return merge(merge3sort(split(m,m.length/3)),merge3sort(split(m,m.length/3)),merge3sort(split(m,m.length/3))); }
}
I get the following exception:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at ololosh1.Ex3.split(Ex3.java:27)
at ololosh1.Ex3.merge3sort(Ex3.java:98)
at ololosh1.Ex3.main(Ex3.java:15)

Look at this part of your code:
for(int i = 0; i<=m.length/3; i++)
third[i]=m[i];
for(int i=0; i<=m.length/3;i++)
third1[i]=m[i+thirdNum];
for(int i=0; i<=m.length/3;i++)
third2[i]=m[i+2*thirdNum];
Arrays are indexed from 0 to length-1. Each third* array has length m.length/3. Therefore their index can only go up to m.length/3 - 1. Yet you are indexing up to and including m.length/3.
Once you get your application working correctly, you really should clean it up. There is a lot of redundancy. For example, you are using the expression m.length/3 multiple times in method split() but you are also passing that same value to it as an argument.

I need help linking my stack Class into my TestBed class

import java.util.Random;
public class TestBed {
public static void main(String a[]) {
// creating the array
int[] array = new int[100];
Random random = new Random();
// changing the variable of my clone array for reference
int[] arr = cloneArray(array);
for (int i1 = 0; i1 < 100; i1++)
array[i1] = random.nextInt(100) + 1;
// print out of bubble sort before and after the sort
System.out
.println("***********************Bubble Sort ****************************");
arr = cloneArray(array);
System.out.println("Values Before the sort:\n");
printArray(arr);
System.out.println();
bubble_srt(arr);
System.out.print("Values after the sort:\n");
printArray(arr);
// print out of selection sort before and after the sort
System.out.println();
System.out
.println("********************Selection Sort*****************************");
System.out.println(" Selection Sort\n\n");
arr = cloneArray(array);
System.out.println("Values Before the sort:\n");
printArray(arr);
System.out.println();
selection_srt(arr);
System.out.print("Values after the sort:\n");
printArray(arr);
System.out.println();
Stack stack = new Stack();
}
public static int[] buildArray(int bound) {
return null;
}
// clone array as a data type
public static int[] cloneArray(int[] data) {
return (int[]) data.clone();
}
// print array as a data type
public static void printArray(int[] data) {
// while there are still numbers left in the array print out the next
// value
for (int i = 0; i < data.length; i++)
System.out.print(data[i] + " ");
}
// bubble syntax
public static void bubble_srt(int a[]) {
int t = 0;
for (int i = 0; i < a.length; i++) {
for (int j = 1; j < (a.length - i); j++) {
if (a[j - 1] > a[j]) {
t = a[j - 1];
a[j - 1] = a[j];
a[j] = t;
}
}
}
}
// selection syntax
public static void selection_srt(int array[]) {
for (int x = 0; x < array.length; x++) {
int index_of_min = x;
for (int y = x; y < array.length; y++) {
if (array[index_of_min] > array[y]) {
index_of_min = y;
}
}
int temp = array[x];
array[x] = array[index_of_min];
array[index_of_min] = temp;
}
}
}
From here i have to link my stack class but i don't know how to get the 2 classes together correctly im new to programming and my school threw me into a java class that was to high for me and now im stuck 5 weeks in.
public class Stack {
Node top;
int size;
public Stack() {
top = null;
size = 0;
}
public int pop() {
if (top != null) {
int item = top.data;
top = top.next;
size--;
return item;
}
return -1;
}
public void push(int data) {
Node t = new Node(data);
t.next = this.top;
this.top = t;
size++;
}
public boolean isEmpty() {
return size <= 0;
}
public int getSize() {
return size;
}
public int peek() {
return top.data;
}
public void printStack() {
Node n = this.top;
int pos = this.getSize();
while (pos > 0) {
System.out.println("Position: " + pos + " Element: " + n.data);
if (pos > 0) {
n = n.next;
}
pos--;
}
}
}
class Node {
public int data;
public Node next;
Node(int d) {
data = d;
next = null;
}
public int getData() {
return data;`enter code here`
}`enter code here`
{
Stack s = new Stack();
s.push(9);
s.push(2);
s.push(7);
s.push(3);
s.push(6);
s.push(4);
s.push(5);
System.out.println("Size is: " + s.getSize());
// s.printStack();
int size = s.getSize();
for (int i = 0; i < size; i++) {
System.out.print(s.pop() + " ");
}
}
}

At the beginning of Stack class file, create a package name, eg:
package com.example.testcode;
Then in your TestBed class file, import your Stack class from the package, eg:
import com.example.testcode.Stack;