QUESTION:

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?

EXPLANATION:

这道题的解法挺多的。我这里采用的是countingsort的方式，计数排序怎么做就不说了，经过了计数排序后其实就已经是结果了。但是需要注意的是最后的结果是校验的nums的值。需要将result的值填充到nums中。

SOLUTION:

class Solution {
    public void sortColors(int[] nums) {
        int[] result = new int[nums.length];
        int[] tmp = new int[3];
        for(int i : nums) tmp[i]++;
        for( int i = 1;i<tmp.length;i++) tmp[i] += tmp[i-1];
        for (int i = nums.length - 1; i > -1; i--) {
            result[tmp[nums[i]] - 1] = nums[i];
            tmp[nums[i]]--;
        }
        for(int i = 0;i<nums.length;i++) nums[i] = result[i];
    }
}