trapping-rain-water

【题目描述】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], return 6.

【解题思路】坐标的最大左右边相减就是该坐标点容积

1. 从左到右扫描，找出每个坐标的最大左值
2. 从右到左扫描，找出每个坐标最大右值
3. 累加每个容积。

【考查内容】数组

class Solution {
public:
    int trap(int A[], int n) {
        if(n<2) 
            return 0;
        int *maxL = new int[n], *maxR = new int[n];
        int maxLR = A[0];
        maxL[0] = 0;
        //from left to right cal max lvalue
        for(int i=1; i<n-1; i++){
            maxL[i] = maxLR;
            if(A[i]>maxLR)
                maxLR = A[i];
        }
        maxLR = A[n-1];
        maxR[n-1] = 0;
        int ttrap = 0, ctrap = 0;
        for(int i=n-2; i>0;i--){
            maxR[i] = maxLR;
            ctrap = min(maxL[i], maxR[i]) - A[i];
            if(ctrap>0)
                ttrap+= ctrap;
            if(maxLR < A[i])
                maxLR = A[i];
        }
        delete maxL, maxR;
        return ttrap;
    }
};