Trapping-rain-water

HowieLee59發表於2018-06-27

題目描述


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], return6.

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!

import java.util.*;
public class Solution {
    public int trap(int[] A) {
        if(A == null || A.length == 0)
        {
            return 0;
        }
        int max = 0;
        int v = 0;
        int[] container = new int[A.length];
        for(int i = 0 ; i<A.length ; i++)
        {
            container[i] = max;
            max = Math.max(max,A[i]);
        }
        max = 0;
        for(int i = A.length - 1; i>=0 ; i--)
        {
            container[i] = Math.min(max,container[i]);
            max = Math.max(max,A[i]);
            v += container[i] - A[i]>0 ? container[i] - A[i] : 0;
        }
        return v;
    }
}