Leetcode75.颜色分类
https://leetcode-cn.com/problems/sort-colors/solution/yan-se-fen-lei-by-leetcode/

class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        p1,p2 = 0,len(nums)-1
        cur = 0
        while cur<=p2:
            if nums[cur] == 0:
                nums[cur], nums[p1] = nums[p1], nums[cur]
                p1 += 1
                cur += 1
            elif nums[cur] == 2:
                nums[cur], nums[p2] = nums[p2], nums[cur]
                p2 -= 1
            else:
                cur += 1