1 class Solution { 2 public: 3     int trap(int A[], int n) { 4         vector<int> max_left(n,0); 5         vector<int> max_right(n,0); 6         int sum = 0; 7         for(int i = 1; i < n; i++){ 8             max_left[i] = max(max_left[i-1], A[i-1]); 9             max_right[n-1-i] = max(max_right[n-i],A[n-i]);10         }11         for(int i = 1; i < n-1; i++){12             int height =  min(max_left[i],max_right[i]);13             if(height > A[i])14                 sum += height - A[i];15         }16         return sum;17     }18 };