【LeetCode】【Python】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?

要求遍历一遍且使用有限的空间，我想了很久都是需要两次遍历或是额外的空间，看了一个思路很简洁的代码，觉得不错分享给大家。但这个代码也有缺点，就是类似于插入排序，需要移动大量元素的位置，时间复杂度也是蛮高的。

class Solution:
    # @param A a list of integers
    # @return nothing, sort in place
    def sortColors(self, A):
        i=j=k=-1
        n=len(A)
        for m in range(n):
            if A[m]==0:
                k=k+1
                A[k]=2
                j=j+1
                A[j]=1
                i=i+1
                A[i]=0
            elif A[m]==1:
                k=k+1
                A[k]=2
                j=j+1
                A[j]=1
            else:
                k=k+1
                A[k]=2