75. Sort Colors

题目：Sort Colors

原题链接：https://leetcode.com/problems/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.

给出一个数组，里面有0，1，2这3种元素，排序让所有的0在前，1在中间，2在最后。
注意，不能使用内置的排序函数。

直接统计数组里面0和1和2的数目，然后把数组的元素重新覆盖一遍就行。

代码如下：

class Solution {
public:
    void sortColors(vector<int>& nums) {
        int len = nums.size(), cnt0 = 0, cnt1 = 0, cnt2 = 0;
        for(int i = 0; i < len; ++i) {
            if(nums[i] == 0) cnt0++;
            else if (nums[i] == 1) cnt1++;
            else cnt2++;
        }
        fill(nums.begin(), nums.begin() + cnt0, 0);
        fill(nums.begin() + cnt0, nums.begin() + cnt0 + cnt1, 1);
        fill(nums.begin() + cnt0 + cnt1, nums.begin() + cnt0 + cnt1 + cnt2, 2);
        return;
    }
};