LeetCode_Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.

For example,
Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!

分析： 对于每一点只需要知道其左边和右边的最高山即可

class Solution {
public:
    int trap(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
         if(n <= ) return ;

        vector<int> left(n,);
        vector<int> right(n, );

        left[] = A[];
        for(int i =; i < n;++i)
        {
          left[i] = left[i-] > A[i] ?  left[i-] : A[i];
        }

        right[n-] = A[n-];
        for(int i = n-; i>= ;--i){
            right[i] = right[i+] > A[i] ? right[i+] : A[i];
        }

        int res = ;
        for(int i = ; i< n; i++){

            int min = left[i] < right[i]? left[i] : right[i];
            res += min - A[i];
        }

        return res;
    }
};