42. 接雨水leetcode

class Solution:
    def trap(self, height: List[int]) -> int:
        n=len(height)
        pre_max= [0]*n
        pre_max[0] =height[0]
        for i in range(1,n):
            pre_max[i]= max(pre_max[i-1],height[i])
        suf_max= [0]*n
        suf_max[-1] =height[-1]
        for i in range(n-2,-1,-1):
            suf_max[i]= max(suf_max[i+1],height[i])
        result = 0
        for i in range(n):
            result += min(pre_max[i],suf_max[i])-height[i]
        return result