trap rain water

class Solution {
public:
    int trap(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if( n==0 )return 0;
        int volum = 0;
        stack<int> s;
        s.push(0);
        int t;
        for(int i=1;i<n;i++)
        {
            if( A[i] == 0 ) continue;
            int h = 0;
            while(!s.empty() )
            {
                t = s.top();
                volum += (i-t-1)*abs( min(A[i], A[t]) - h );
                if( A[i] >= A[t] )
                {
                    s.pop();
                //    s.push(i);
                    h = A[t];
                }
                else
                    break;              
            }   
            s.push(i);
        }
        return volum;
        
    }
};