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: //夹逼准则。每次让低的那一侧移动。直到相遇 int trap(vector<int>& height) { int low=0,high=height.size()-1,res=0; int leftmax=0,rightmax=0; while(low<=high){ if(height[low]<height[high]){ leftmax=max(leftmax,height[low]); res+=leftmax-height[low]; low++; } else { rightmax=max(rightmax,height[high]); res+=rightmax-height[high]; high--; } } return res; } };
原文：http://www.cnblogs.com/tsunami-lj/p/6675325.html