leetcode 75. Sort Colors 荷兰国旗

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?

Accepted

349,504

Submissions

811,345

标准写法：

class Solution:
    def sortColors(self, nums: List[int]) -> None:
        l,cur,r = 0,0,len(nums)-1
        while (cur <= r):
            if (nums[cur] == 0):
                nums[l],nums[cur]=nums[cur],nums[l]
                l,cur = l+1,cur+1
            elif (nums[cur] == 2):
                nums[r],nums[cur]=nums[cur],nums[r]
                r -= 1
            else:
                cur += 1