颜色分类

输入: [2,0,2,1,1,0]
输出: [0,0,1,1,2,2]

class Solution:
    def sortColors(self, nums: List[int]) -> None:
        '''
        荷兰三色旗问题解
        '''
        # 对于所有 idx < p0 : nums[idx < p0] = 0
        # curr是当前考虑元素的下标
        p0 = curr = 0
        # 对于所有 idx > p2 : nums[idx > p2] = 2
        p2 = len(nums) - 1
      while curr <= p2:
          if nums[curr] == 0:
              nums[p0], nums[curr] = nums[curr], nums[p0]
              p0 += 1
              curr += 1
          elif nums[curr] == 2:
              nums[curr], nums[p2] = nums[p2], nums[curr]
              p2 -= 1
          else:
              curr += 1