[leetCode] 75. Sort Colors (Python)

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?

Solution

from collections import Counter
class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        
        nums_dict = dict(Counter(nums))
        
        keys = nums_dict.keys()
        
        index = 0
        for i in range(3):
            if i in keys:
                for j in range(nums_dict[i]):
                    nums[index] = i
                    index = index + 1

 

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