目录

1，题目描述

2，思路

3，代码【C++】

1，题目描述

Given an array with n objects colored red, white or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note: You are not suppose to use the library's sort function for this problem.

Example:

Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Follow up:

    A rather straight forward solution is a two-pass algorithm using counting sort.
    First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's, then 1's and followed by 2's.
    Could you come up with a one-pass algorithm using only constant space（常数空间）?

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/sort-colors
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2，思路

emmm，有图有真相，就不多说了。。。

时间复杂度O(n)

最后

3，代码【C++】

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int left = 0, mid = 0, right = nums.size() - 1;
        while(mid <= right){
            if(nums[mid] == 0){
                swap(nums, left, mid);
                left++;mid++;
            }
            else if(nums[mid] == 1){
                mid++;
            }
            else{
                swap(nums, mid, right);
                right--;
            }
        }
    }

    void swap(vector<int>& nums, int i, int j){
        int temp ;
        temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
};