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!

class Solution {
public:
    int trap(int A[], int n) 
    {
        int count=0;
        if(n<=2) return count;
        
        int h[n];h[0]=A[0];
        for(int i=1;i<n;i++)
            if(A[i]>h[i-1]) h[i]=A[i];
            else h[i]=h[i-1];
        h[n-1]=A[n-1];
        for(int i=n-2;i>=0;i--)
        {
            if(h[i]<=h[i+1]) break;
            
            if(A[i]>h[i+1]) h[i]=A[i];
            else h[i]=h[i+1];
        }
        
        for(int i=0;i<n;i++)
            count=count+h[i]-A[i];
        
        return count;
    }
};