class Solution:
    def trap(self, height: List[int]) -> int:
        maxleft = [0]*len(height)
        maxright = [0]*len(height)
        for i in range(0,len(height)):
            if i == 0:
                maxleft[i] = 0
            else:
                maxleft[i] = max(maxleft[i-1],height[i-1])
            now = len(height) - i - 1
            if now == len(height) - 1:
                maxright[now] = 0
            else:
                maxright[now] = max(maxright[now+1],height[now+1])
        
        ans = 0
        for i in range(1,len(height) - 1):
            temp = min(maxleft[i],maxright[i])
            if temp > height[i]:
                ans += temp - height[i]
        return ans