java快速排序(快排)算法Quicksort

public class Test {

    public static void main(String[] args) {
        int[] a = {5, 2, 6, 9, 1, 3, 7,4,0,8};
        printIntArray(a);
        qsort(a, 0, a.length - 1);
        printIntArray(a);


    }

    public static void qsort(int[] a, int left, int right) {
        if (left>right) return ;
        int left_pointer = left;
        int right_pointer = right;
        int key = a[left];
        while (left_pointer < right_pointer) {
            while (left_pointer < right_pointer && key < a[right_pointer]) {//从右边开始找小于key的值
                right_pointer--;
            }
            a[left_pointer] = a[right_pointer];//如果找到交换，否则就是left_pointer = right_pointer
            while (left_pointer < right_pointer && key > a[left_pointer]) {
                left_pointer++;
            }
            a[right_pointer] = a[left_pointer];
        }
        a[left_pointer] = key;//一趟排序完毕，key放入指针位置，这时left_pointer = righ_pointer，key左边都比它小，右边都比它大，然后各自递归左右两边
        qsort(a, left, left_pointer - 1);
        qsort(a, left_pointer + 1, right);
    }

    public static void printIntArray(int[] a) {
        for (int i : a) {
            System.out.print(i + " ");
        }
        System.out.println("");
    }
}