Leetcode 75. Sort Colors

标签：library   tps   ref   strong   repr   等于   array   交换   overwrite   

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?

解法一很直观，只要扫描一遍nums，把里面有多少个0,1,2记录下来就行了。

OJ要求one-pass，参考了喜刷刷的解法。假设当前的情况如下：

 1 class Solution(object):
 2     def sortColors(self, nums):
 3         """
 4         :type nums: List[int]
 5         :rtype: void Do not return anything, modify nums in-place instead.
 6         """
 7         n = len(nums)
 8         left = 0
 9         right = n - 1
10         i = 0
11         
12         while i <= right:
13             if nums[i] == 0:
14                 nums[i], nums[left] = nums[left], nums[i]
15                 left += 1
16                 i += 1
17             elif nums[i] == 2:
18                 nums[i], nums[right] = nums[right], nums[i]
19                 right -= 1
20             else:
21                 i += 1

Leetcode 75. Sort Colors

标签：library   tps   ref   strong   repr   等于   array   交换   overwrite   

原文地址：http://www.cnblogs.com/lettuan/p/6258648.html