leetcode - 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!
class Solution { public: int trap(int A[], int n) { if(n <=2) return 0; int t = 0; int l = A[0], r=A[n-1]; int bgn = 1, end = n-2; while(bgn <= end){ if(l < r){ t += std::max(l - A[bgn], 0); l = std::max(l, A[bgn]); bgn++; } else{ t += std::max(r - A[end], 0); r = std::max(r, A[end]); end--; } } return t; } };