LeetCode 042 Trapping Rain Water

题目要求：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!

 

代码如下：

class Solution {

public:

    int trap(int A[], int n) {

        

        int maxIdx = 0;

        int water = 0;

        

        //找到最长的木板，设为maxIdx

        for(int i = 1; i < n; i++){

            if(A[i] > A[maxIdx]){

                maxIdx = i;

            }

        }

        

        int max = A[0];

        

        //左侧逼近

        for(int i = 1; i < maxIdx; i++){

            

            if(max < A[i]) 

                max = A[i];

            //木板左边(max)和右边(最高)都比它高，则可以放

            // max - 该木板长度 的水

            else 

                water += max - A[i];

        }

        

        //右侧逼近

        max = A[n - 1];

        for(int i = n - 2; i >= maxIdx; i--){

            if(max < A[i]) max = A[i];

            else water += max - A[i];

        }

        

        return water;

        

    }

};