75_sortColors.py
class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        i,j,k = 0,len(nums)-1,0
        while k<len(nums):
            if nums[k] ==0 and k>i:
                nums[k],nums[i]=nums[i],nums[k]
                i += 1
            elif nums[k] == 2 and k<j:
                nums[k],nums[j]=nums[j],nums[k]
                j -= 1
            else:
                k += 1
