QuickSort.java

import java.util.Arrays;

public class QuickSort {

    public static int findPivot(int[] arr, int lo, int hi) {
        int pivot = arr[hi];
        int boundary = lo - 1;
        for (int i = lo; i < hi; i++) {
            if (arr[i] <= pivot) {
                boundary++;
                swap(arr, boundary, i);
            }
        }
        ++boundary;
        swap(arr, hi, boundary);
        return boundary;
    }

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

    public static void quickSort(int[] arr, int lo, int hi){
        if (lo < hi) {
            int pivot = findPivot(arr, lo, hi);
            quickSort(arr, lo, pivot - 1);
            quickSort(arr, pivot+1, hi);
        }
    }

    public static void main(String[] args) {
        int[] arr = new int[] { -1, 1, 3, 2, 4, 0, 1 };

        // System.out.println(findPivot(arr, 0, arr.length - 1));
        // System.out.println(Arrays.toString(arr));

        quickSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }
}