1. /**
    2.      * https://wiki.jikexueyuan.com/project/easy-learn-algorithm/fast-sort.html
    3.      * 快速排序
    4.      * @param arr
    5.      * @param i
    6.      * @param j
    7.      */
    8. public static void quickSort(int[] arr, int i, int j){
    9.     if (i>j) {
    10.         return;
    11.     }
    12.     int pivot = arr[i];
    14.     int left=i;
    15.     int right=j;
    17.     while (left!=right) {
    18.         while ((right>left)&&arr[right] >= pivot) {
    19.             right--;
    20.         }
    21.         //此时a[right]小于pivot
    23.         while ((left < right)&&arr[left] <= pivot) {
    24.             left++;
    25.         }
    26.         //此时a[left]大于pivot
    28.         //交换a[i] a[j]
    29.         if (left < right) {
    30.             swap(arr, left, right);
    31.         }
    32.     }
    33.     arr[i] = arr[left];
    34.     arr[left]=pivot;
    36.     quickSort(arr,i,left-1);
    37.     quickSort(arr,left+1,j);
    38. }
    40. public static void quickSort(int[] arr) {
    41.     quickSort(arr,0,arr.length-1);
    42. }
    44. private static void swap(int[] arr, int idx1,int idx2) {
    45.     int tmp = arr[idx2];
    46.     arr[idx2] = arr[idx1];
    47.     arr[idx1] = tmp;
    48. }