Sort Colors

Given an array with n objects colored red, white or blue, sort them 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.

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hint: 使用快速排序分区的单向扫描法

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int left_index = -1;
        int right_index = nums.size();
        for (int i = 0; i < right_index;) {
            if (nums[i] == 0) {
                swap(nums[++left_index], nums[i]);
                ++i;
            } else if (nums[i] == 2) {
                swap(nums[--right_index], nums[i]);
            } else {
                ++i;
            }
        }
    }
};