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

class Solution:
    def trap(self, height: List[int]) -> int:
        n=len(height)
        pre_max=0
        suf_max=0 
        left =0
        right=n-1
        ans=0
        while left<=right:
            pre_max=max(pre_max,height[left])
            suf_max=max(suf_max,height[right])
            if pre_max<suf_max:
                ans +=pre_max-height[left]
                left += 1
            else:
                ans +=suf_max-height[right]
                right -=1
        return ans