sort-colors

1、来源：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?

2、思路：

• 我的实现直接分别1遍，记录0和2的个数，然后前面赋值0，后面赋值2，剩下的赋值1；但是题目明确说明了“an one-pass algorithm”
• 看了答案区，设置0指针zeroindex=0，设置2指针twoindex=len -1，i指向当前元素，然后开始遍历数组，如果遍历到0则swap（zeroindex，i），i++和zeroindex++，如果是2则swap（twoindex，i）twoindex–，i++，如果是1，则i++

3、代码：

public void sortColors(int[] A) {        int len = A.length;        int zero_num = 0;        int one_num = 0;        for(int t:A){            if(t == 0)                zero_num++;            if(t == 1)                one_num++;        }        int i;        for(i = 0; i < zero_num; i++)            A[i] = 0;        int sum = zero_num + one_num;        for(; i < sum; i++)            A[i] = 1;        for(;i < len; i++)            A[i] = 2;    }