sortColors.py

"""
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.

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

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?

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

"""

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

# Time Complexity = O(n)
# Space Complexity = O(1)