[Leetcode题解]接雨水

42. 接雨水

思路

from typing import List
import bisect


class Solution:
    def trap(self, height: List[int]) -> int:

        def helper(height, reverse=False):
            index, ans, left_max_h_index, n, water = 0, 0, 0, len(height), 0

            if reverse: height.reverse()
            height, n = height + [0], n + 1

            for index, h in enumerate(height):
                if index == 0 or index == n - 1: continue
                # 可以做右边界
                if h >= height[index + 1] and h >= height[index - 1] and height[left_max_h_index] <= h:
                    # 左边最高的比他低，那么一定会形成一个区间。
                    ans += water
                    left_max_h_index = index
                    water = 0
                else:
                    water += max(0, (height[left_max_h_index] - h))
            return ans, left_max_h_index

        x, left_max_h_index = helper(height)
        y, _ = helper(height[left_max_h_index:], reverse=True)
        return x+y