Sort Colors

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?

题目要求是原址的，思想就是:遇到2就交换到末尾，遇到0,就交换的前面，直至开始和结束两指针相遇。

https://discuss.leetcode.com/topic/36832/sharing-c-solution-with-good-explanation

    1 0 2 2 1 0    ^         ^    L         H    M    Mid != 0 || 2    Mid++    1 0 2 2 1 0    ^ ^       ^    L M       H    Mid == 0    Swap Low and Mid    Mid++    Low++    0 1 2 2 1 0      ^ ^     ^      L M     H    Mid == 2    Swap High and Mid    High--    0 1 0 2 1 2      ^ ^   ^      L M   H    Mid == 0    Swap Low and Mid    Mid++    Low++    0 0 1 2 1 2        ^ ^ ^        L M H    Mid == 2    Swap High and Mid    High--    0 0 1 1 2 2        ^ ^        L M          H    Mid <= High is our exit case