LeetCode-75.Sort Colors

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.

click to show follow up.

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 an one-pass algorithm using only constant space?

方法1 

使用计数排序，先统计不同color(0，1，2)的个数，然后再对原始数组赋值

void sortColors(vector<int>& nums)    {        int color[3];        color[0] = color[1] = color[2] = 0;        int n = nums.size();        for (int i = 0; i < n; i++)        color[nums[i]]++;        int k = 0;        for (int i = 0; i < 3; i++)        {        while (color[i]-->0)        nums[k++] = i;        }    }

方法2

使用双指针一次扫描，参考 http://blog.csdn.net/linhuanmars/article/details/24286349

void sortColors(vector<int>& nums)    {        int p0 = 0, p1 = 0,n = nums.size();        for (int i = 0; i < n; i++)        {        if (nums[i] == 0)        {        nums[i] = 2;        nums[p1++] = 1;        nums[p0++] = 0;        }        else if (nums[i] == 1)        {        nums[i] = 2;        nums[p1++] = 1;        }        }    }