text: #!/usr/bin/env python
  # coding=utf-8
  '''
  Author: John
  Email: johnjim0816@gmail.com
  Date: 2020-08-02 14:52:55
  LastEditor: John
  LastEditTime: 2020-08-02 14:53:54
  Discription: 
  Environment: 
  '''
  # Source : https://leetcode.com/problems/sort-colors/
  # Author : JohnJim0816
  # Date   : 2020-08-02
  
  ##################################################################################################### 
  #
  # 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?
  # 
  #####################################################################################################
  
  class Solution:
      def sortColors(self, nums: List[int]) -> None:
          '''
          荷兰三色旗问题解
          '''
          # 对于所有 idx < p0 : nums[idx < p0] = 0
          # curr是当前考虑元素的下标
          p0 = curr = 0
          # 对于所有 idx > p2 : nums[idx > p2] = 2
          p2 = len(nums) - 1
  
          while curr <= p2:
              if nums[curr] == 0:
                  nums[p0], nums[curr] = nums[curr], nums[p0]
                  p0 += 1
                  curr += 1
              elif nums[curr] == 2:
                  nums[curr], nums[p2] = nums[p2], nums[curr]
                  p2 -= 1
              else:
                  curr += 1