LeetCode75 Sort Colors 色彩排序 C++

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本文介绍了一个不使用排序库函数的三色排序问题解决方案。通过在原地修改数组，确保相同颜色的对象相邻，并按红、白、蓝的顺序排列。文中提供了一种仅使用常数空间的一遍算法实现。

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问题描述：
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?
题源：here；完整实现：here
思路：
将0往与靠前面的位置交换，2与靠后面的位置交换，代码如下：

    void sortColors(vector<int>& nums) {
        int left = -1, right = nums.size();
        int idx = 0;
        while (idx < right){
            if (nums[idx] == 0) swap(nums[++left], nums[idx]);
            if (nums[idx] == 2) swap(nums[--right], nums[idx]);
            else idx++;
        }
    }