Quick.java

import java.util.Arrays;

public class Quick {
    public static void main(String[] args) {
        int[] arr = {5,4,3,2,1};
        quick(arr, 0, arr.length-1);
        System.out.println(Arrays.toString(arr));
    }

    static void quick(int[] arr, int low, int hi){
        if(low>=hi){
            return;
        }
        int s = low;
        int e = hi;
        int m = s+(e-s)/2;
        int p = arr[m];
        while(s<=e){
            while(arr[s]<p){
                s++;
            }
            while(arr[e]>p){
                e--;
            }
            if(s<=e){
                int temp = arr[s];
                arr[s] = arr[e];
                arr[e] = temp;
                s++;
                e--;
            }
        }

        quick(arr, low, e);
        quick(arr, s, hi);
    }
}