题目描述：
    image.png
    image.png
    解析：双指针 <1左边 =1中间 >1右边

    1. class Solution {
    2.     public void sortColors(int[] nums) {
    3.         int less = -1, more = nums.length, index = 0;
    4.         while (index != more) {  //循环终止条件
    5.             if (nums[index] > 1) {
    6.                 swap(nums, index, --more);
    7.             } else if (nums[index] < 1) {
    8.                 swap(nums, ++less, index++);
    9.             } else {
    10.                 index++;
    11.             }
    12.         }
    13.     }
    14.     private void swap(int[] arr, int p1, int p2) {
    15.         int tmp = arr[p1];
    16.         arr[p1] = arr[p2];
    17.         arr[p2] = tmp;
    18.     }
    19. }