快速排序

public class QuickSort {
    public static void main(String[] args) {
//        int[] arr = {2, 4, 1, 6, 1, 3, 9};
        int[] arr = {2, 2, 2, 1, 1, 1, 1};
        quickSort(arr,0,arr.length-1);
        System.out.println(Arrays.toString(arr));
    }

    private static void quickSort(int[] arr, int start, int end){
        if(start < end){
            //找到基准数
            int standard = arr[start];
            //定义两个指针
            int low = start;
            int high = end;
            //循坏查找比基准小的数字和比基准数大的数
            while(low < high){
                //如果右边数比基准数大，就指针向前移
                while(low < high && arr[high] >= standard){
                    high--;
                }
                //把值赋给左边的
                arr[low] = arr[high];

                //如果左边的比基准值小，指针向后移
                while(low < high && arr[low] <= standard){
                    low++;
                }
                //把值赋给右边
                arr[high] = arr[low];
            }
            //循坏结束，low和high相等，把基准值赋给他
            arr[low] = standard;

            //排左边
            quickSort(arr,start,low);

            //排右边
            quickSort(arr,low+1,end);
        }

    }
}