How to perform quick sort, in Java?

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/*
	This is an implementation of the quick sort algorithm.

	Let n be the size of the list to sort
	Best: O(nlog2(n)) time | O(log2(n)) space
	Average: O(nlog2(n)) time | O(log2(n)) space
	Worst: O(n^2) time | O(log2(n)) space
*/
import java.util.Arrays;

public class QuickSort {
	public static void main(String[] args) {
		int[] arr = { 1, 10, 5, 3, 6 };
		quickSort(arr);
		// Below prints: [1, 3, 5, 6, 10]
		System.out.println(Arrays.toString(arr));
	}

	public static void quickSort(int[] array) {
		// Sort array recursively
		quickSortUtil(array, 0, array.length - 1);
	}

	private static void quickSortUtil(int[] array, int startIdx, int endIdx) {
		// Base case: at this point array is sorted
		if (startIdx >= endIdx) {
			return;
		}
		// Let first value be pivot
		// Sort every other number wrt to pivot
		int pivotIdx = startIdx;
		int leftIdx = startIdx + 1;
		int rightIdx = endIdx;
		// Make sure that element at leftIdx <= to one at pivotIdx
		// and element at rightIdx is >= to one at pivotIdx
		while (leftIdx <= rightIdx) {
			if (array[leftIdx] > array[pivotIdx] && array[rightIdx] < array[pivotIdx]) {
				swap(leftIdx, rightIdx, array);
			}
			if (array[leftIdx] <= array[pivotIdx]) {
				leftIdx++;
			}
			if (array[rightIdx] >= array[pivotIdx]) {
				rightIdx--;
			}
		}

		swap(pivotIdx, rightIdx, array);
		// At the end of current iteration, element at
		// pivot is in its final sorted position
		quickSortUtil(array, startIdx, rightIdx - 1);
		quickSortUtil(array, rightIdx + 1, endIdx);
	}

	private static void swap(int i, int j, int[] array) {
		int temp = array[i];
		array[i] = array[j];
		array[j] = temp;
	}
}

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Source: Grepper

Tags: java

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Contributed on May 26 2022

Wissam

0 Answers Avg Quality 2/10

java quick sort

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import java.util.Arrays;
//so fun to run//try it (;
//Illustrate array in size of 100 Million Integers 
//global arrays only!!
public class Quick {
    static int[] arr = new int[10000000];
    public static void main(String[] args) {//only use with global array!
       
        for(int i=0; i<arr.length;i++){
            arr[i]= (int)(Math.random()*1000);
        }
        quickSort(0, arr.length-1, arr[arr.length-1]);
       //(send 0 to lowi,
      //send the last index in the array to higi, 
      //send to pivot the last value in the array)
       System.out.println(Arrays.toString(arr));
         
    }
    public static void quickSort(int lowi,int higi,int pivot){
        if(higi<=lowi)
          return;
        if(higi - lowi <1)
           return;
        if(higi - lowi == 1){
            if(arr[lowi]>arr[higi])
               swap(lowi, higi);
                 return;
        }
        int temp, next = arr[lowi];
        int higiS = higi, lowiS = lowi,pos = lowi;
        
        while(higi-lowi >= 1){
            if(next<pivot){
                 temp = arr[higi];
                 if(higi == higiS)
                   temp = arr[++pos];
                 else
                   temp = arr[higi];
                
                arr[higi--] = next; 
                }
            else{
                if(lowi<=pos)
                  temp = arr[++pos];
                else
                  temp = arr[lowi];
                
                arr[lowi++] = next;
                }
                next = temp;
            }
            if(lowi<pos)
              lowi = pos-1;
      
        arr[lowi] = pivot;
        
        quickSort(lowi+1, higiS, arr[higiS]);
        if(lowi-1>=0)
        quickSort(lowiS, lowi-1, arr[lowi-1]);
 
        return;
    }
    public static void swap(int fI,int sI){
        int temp = arr[fI];
        arr[fI] = arr[sI];
        arr[sI] = temp;
    }
   
}

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Source: Grepper

Tags: java

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Contributed on May 06 2022

Elegant Elephant

0 Answers Avg Quality 2/10

Quick Sort Java Implementation

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// Java implementation of QuickSort
import java.io.*;
 
class GFG{
     
// A utility function to swap two elements
static void swap(int[] arr, int i, int j)
{
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}
 
/* This function takes last element as pivot, places
   the pivot element at its correct position in sorted
   array, and places all smaller (smaller than pivot)
   to left of pivot and all greater elements to right
   of pivot */
static int partition(int[] arr, int low, int high)
{
     
    // pivot
    int pivot = arr[high];
     
    // Index of smaller element and
    // indicates the right position
    // of pivot found so far
    int i = (low - 1);
 
    for(int j = low; j <= high - 1; j++)
    {
         
        // If current element is smaller
        // than the pivot
        if (arr[j] < pivot)
        {
             
            // Increment index of
            // smaller element
            i++;
            swap(arr, i, j);
        }
    }
    swap(arr, i + 1, high);
    return (i + 1);
}
 
/* The main function that implements QuickSort
          arr[] --> Array to be sorted,
          low --> Starting index,
          high --> Ending index
 */
static void quickSort(int[] arr, int low, int high)
{
    if (low < high)
    {
         
        // pi is partitioning index, arr[p]
        // is now at right place
        int pi = partition(arr, low, high);
 
        // Separately sort elements before
        // partition and after partition
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}
 
// Function to print an array
static void printArray(int[] arr, int size)
{
    for(int i = 0; i < size; i++)
        System.out.print(arr[i] + " ");
         
    System.out.println();
}
 
// Driver Code
public static void main(String[] args)
{
    int[] arr = { 10, 7, 8, 9, 1, 5 };
    int n = arr.length;
     
    quickSort(arr, 0, n - 1);
    System.out.println("Sorted array: ");
    printArray(arr, n);
}
}
 
// This code is contributed by Ayush Choudhary

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Source: www.geeksforgeeks.org

Tags: implementation impl

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Contributed on Mar 10 2022

Stupid Scarab

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quicksort java

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//GOD's quicksort
public static <E extends Comparable<E>> List<E> sort(List<E> col) {
  if (col == null || col.isEmpty())
    return Collections.emptyList();
  else {
    E pivot = col.get(0);
    Map<Integer, List<E>> grouped = col.stream()
      .collect(Collectors.groupingBy(pivot::compareTo));
    return Stream.of(sort(grouped.get(1)), grouped.get(0), sort(grouped.get(-1)))
      .flatMap(Collection::stream).collect(Collectors.toList());
  }
}

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Source: rosettacode.org

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Contributed on Apr 26 2021

Yellowed Yacare

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java array quick sort

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void selectionSort(int arr[])
{
    int n = arr.length;

    for (int i = 0; i < n-1; i++)
    {
        int min_idx = i;
        for (int j = i+1; j < n; j++)
            if (arr[j] < arr[min_idx])
                min_idx = j;

        int temp = arr[min_idx];
        arr[min_idx] = arr[i];
        arr[i] = temp;
    }
}

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Source: www.sortvisualizer.com

Tags: java

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Contributed on Jun 12 2022

Homeless Hummingbird

0 Answers Avg Quality 2/10

quicksort java

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import java.util.Random;

public class main{
public static void main(String[] args) {
    Random rand=new Random();
    int[]numbers=new int[60000000];
    for (int i = 0; i < numbers.length; i++) {
        numbers[i]=rand.nextInt(10000);
    }
    System.out.println("before");
    quickSort(numbers);
    System.out.println("after");
   // printArray(numbers);
    
}
static void printArray(int []numbers){
    for(int x:numbers){
        System.out.println(x);
    }
}
static void quickSort(int[]numbers){
    quickSort(numbers,0,numbers.length-1);
}
static void quickSort(int[]numbers,int lowIndex,int heighIndex){
if(lowIndex>=heighIndex)return;
int pivotIndex=new Random().nextInt(heighIndex-lowIndex)+lowIndex;
int pivot=numbers[pivotIndex];
int leftPointer=lowIndex;
int righPointer=heighIndex;
swap(numbers, pivotIndex, heighIndex);
while(leftPointer<righPointer){
    while(numbers[leftPointer]<=pivot&&leftPointer<righPointer){
        leftPointer++;
    }
    while(numbers[righPointer]>=pivot&&leftPointer<righPointer){
        righPointer--;
    }
    swap(numbers,leftPointer, righPointer);
}
swap(numbers, leftPointer,heighIndex);
quickSort(numbers,lowIndex,leftPointer-1);
quickSort(numbers, leftPointer+1, heighIndex);

}
static void swap(int[]numbers,int index1,int index2){
int  temp=numbers[index1];
numbers[index1]=numbers[index2];
numbers[index2]=temp;
}
    

 }

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Source: Grepper

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Contributed on Jun 03 2022

La Van Tho

0 Answers Avg Quality 2/10

quick sort java

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import java.util.*;

public class Sort {
    static ArrayList<Integer> quicksort(ArrayList<Integer> list) {
        if (list.size() <= 1) {
            return list;
        }
        ArrayList<Integer> lessThanPivot = new ArrayList<Integer>();
        ArrayList<Integer> greaterThanPivot = new ArrayList<Integer>();
        int pivot = list.get(0);
        int length = list.size();
        for (int i = 1; i < length; i++) {
            int currentValue = list.get(i);
            if (currentValue <= pivot) {
                lessThanPivot.add(currentValue);
            } else {
                greaterThanPivot.add(currentValue);
            }
        }
        ArrayList<Integer> sortedList = new ArrayList<Integer>();
        sortedList.addAll(quicksort(lessThanPivot));
        sortedList.add(pivot);
        sortedList.addAll(quicksort(greaterThanPivot));
        return sortedList;
    }

    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<Integer>(Arrays.asList(32, 100, 1, 2, 29, 28, 88, 3, 50, 67, 37, 1, 57, 20));
        System.out.println(quicksort(list));
    }
}

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Contributed on Nov 18 2022

Xanthous Xenomorph

0 Answers Avg Quality 2/10

quicksort java

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static int partition(int[] array , int low , int high){
                int i = (low - 1)  ;
                int pivot = array[high] ;
                for(int j = low ; j < high ; ++j){
                        if(array[j] <= pivot){
                                ++i ;
                                int temp  = array[i] ;
                                array[i] = array[j] ;
                                array[j] = temp ;
                        }
                }
                int temp = array[i+1] ;
                array[i+1]= array[high] ;
                array[high] = temp ;
                return (i+1) ;
        }

        static void QuickSort(int[] array , int low , int high){
                if (low < high) {
                        int pi = partition(array , low , high) ;
                        QuickSort(array , low , pi - 1) ;
                        QuickSort(array , pi + 1 , high) ;
                }
        }

 public static void main(String[] args) {
    QuickSort(arr , 0 , arr.length -1) ;
 }

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Source: Grepper

Tags: java quicksort

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Contributed on Aug 24 2023

Win_IT

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quick sort in java progrmmieren

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package quickSort;

import java.util.Arrays;

public class Main {

    private int[] A;

    public int[] getA() {
        return A;
    }

    public void setA(int[] a) {
        A = a;
    }

    public static void main(String[] args) {
        Main a = new Main();
        int[] A = {2, 1, 9, 7, 4, 8, 10, 5, 6, 3};
        a.setA(A);
        a.quickSort(0, A.length-1);
        System.out.println(Arrays.toString(a.getA()));
    }

    public void quickSort(int l, int r){
        if(l < r){System.out.println(Arrays.toString(getA()));
            int m = partition(l, r);
            System.out.println(getA()[m]);
            quickSort(l, m-1);System.out.println(Arrays.toString(getA()));
            quickSort(m+1, r);System.out.println(Arrays.toString(getA()));

        }
    }

    public int partition(int l, int r) {
        int pivot = getA()[r];
        int i = l;
        for(int j = l; j < r; j++){
            if(getA()[j] <= pivot){
                swap(i, j);
                i++;
            }
        }
        swap(i, r);
        return i;
    }

    public void swap(int i, int r){
        int[] A = getA();
        int lel = A[i];
        A[i] = A[r];
        A[r] = lel;
        setA(A);
    }
}

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Contributed on Dec 14 2021

znarfbay

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quick Sort in java

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// Quick sort in Java

import java.util.Arrays;

class Quicksort {

  // method to find the partition position
  static int partition(int array[], int low, int high) {
    
    // choose the rightmost element as pivot
    int pivot = array[high];
    
    // pointer for greater element
    int i = (low - 1);

    // traverse through all elements
    // compare each element with pivot
    for (int j = low; j < high; j++) {
      if (array[j] <= pivot) {

        // if element smaller than pivot is found
        // swap it with the greatr element pointed by i
        i++;

        // swapping element at i with element at j
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
      }

    }

    // swapt the pivot element with the greater element specified by i
    int temp = array[i + 1];
    array[i + 1] = array[high];
    array[high] = temp;

    // return the position from where partition is done
    return (i + 1);
  }

  static void quickSort(int array[], int low, int high) {
    if (low < high) {

      // find pivot element such that
      // elements smaller than pivot are on the left
      // elements greater than pivot are on the right
      int pi = partition(array, low, high);
      
      // recursive call on the left of pivot
      quickSort(array, low, pi - 1);

      // recursive call on the right of pivot
      quickSort(array, pi + 1, high);
    }
  }
}

// Main class
class Main {
  public static void main(String args[]) {

    int[] data = { 8, 7, 2, 1, 0, 9, 6 };
    System.out.println("Unsorted Array");
    System.out.println(Arrays.toString(data));

    int size = data.length;

    // call quicksort() on array data
    Quicksort.quickSort(data, 0, size - 1);

    System.out.println("Sorted Array in Ascending Order: ");
    System.out.println(Arrays.toString(data));
  }
}

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Contributed on Dec 11 2022

Jittery Jellyfish

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How to perform quick sort, in Java?

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