75. Sort Colors

Medium

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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.

You must solve this problem without using the library's sort function.

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]

Constraints:

• n == nums.length

• 1 <= n <= 300

• nums[i] is either 0, 1, or 2.

Follow up: Could you come up with a one-pass algorithm using only constant extra space?

class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        left = 0
        mid = 0
        right = len(nums) - 1
        while mid <= right:
            if nums[mid] == 0:
                nums[left], nums[mid] = nums[mid], nums[left]
                mid += 1
                left += 1
            elif nums[mid] == 1:
                mid += 1
            else:
                nums[right], nums[mid] = nums[mid], nums[right]
                right -= 1