Sort Color @leetcode

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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.

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?

» Solve this problem

使用enhanced quicksort. 用两个mark变量标记０和２所在的位置。先左边，和右边把０和２找尽。之后用一个Ｐ变量一个一个找，遇到１不动，遇到０或２交换。

中间有一个特别重要的细节要注意，因为交换完了之后容易导致一些０或２漏掉，这个时候要加条件判断。