Leetcode - Sort Colors Solution

Given an array nums 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.

We will use the integers 0, 1, and 2 to represent the color red, white, and blue, respectively.

Example 1:

Input: nums = [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Example 2:

Input: nums = [2,0,1]
Output: [0,1,2]

Example 3:

Input: nums = [0]
Output: [0]

Example 4:

Input: nums = [1]
Output: [1]

Constraints:

• n == nums.length
• 1 <= n <= 300
• nums[i] is 0, 1, or 2.

Follow up:

• Could you solve this problem without using the library's sort function?
• Could you come up with a one-pass algorithm using only O(1) constant space?

Solution in Python

from collections import Counter
class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        count = Counter(nums)
        index = 0
        for i in [0,1,2]:
            while count[i]:
                nums[index] = i
                count[i] -= 1
                index+=1