leetcode:Trapping Rain Water

class Solution {public:    int trap(int A[], int n) {        if(n <= 0)            return 0;        int * water = new int[n];        int current =0;        for(int i=0 ;i<n;i++)        {            current = max(current,A[i]);            water[i] = current;        }        current = 0;        for(int i =n-1;i>=0;i--)        {            current = max(current,A[i]);            water[i] = min(water[i],current);        }        int result = 0;        for(int i =0; i < n;i++)        {            result += water[i]-A[i];        }        delete [] water;        return result;    }};