Quick Sort

Quick sort

Algorithm

low, high => represents start and end index of array
quickSort(arr[], low, high){
if(low < high){
pi = partition(arr, low, high);
quickSort(arr, low, pi – 1);
quickSort(arr, pi + 1, high);
}
}

Code

package sorting;

import java.util.Arrays;

/**
 * low, high => represents start and end index of array
 * quickSort(arr[], low, high){
 *     if(low < high){
 *         pi = partition(arr, low, high);
 *         quickSort(arr, low, pi - 1);
 *         quickSort(arr, pi + 1, high);
 *     }
 * }
 *
 *                            { 5, 4, 3, 2, 1, 6, 7}
 *                                /      \
 *                       {4, 3, 2, 1}   {6, 7}
 *                       /      \         /  \
 *                 {3, 2, 1}    { }     { }  {7}
 *                   /    \
 *               {2, 1}   { }
 *               /   \
 *             {1}  { }
 */
public class QuickSort {
    public static void main(String[] args) {
        int[] arr = new int[]{5,4,3,2,1, 23,1, 23};
        quickSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }

    static void quickSort(int[] arr, int low, int high){
        if(low < high) {
            int pivot = partition(arr, low, high);
            quickSort(arr, low, pivot - 1);
            quickSort(arr, pivot + 1, high);
        }
    }

    static int partition(int[] arr, int low, int high){

        int i = low + 1;
        int pi = low;
        while(i < high){

            if(arr[i] < arr[low]){
                int temp = arr[i];
                arr[i] = arr[low];
                arr[low] = temp;
                low++;
                pi= i;
            }
            i++;

        }

        int temp = arr[pi];
        arr[pi] = arr[low];
        arr[low] = temp;
        return low + 1;

    }
}
java