Leetcode trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar are 1, compute how much WA ter It is the 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 the Rain Water (blue section) is being trapped. Thanks Marcos for contributing this image!

Test instructions: Find out how much water is loaded.

Idea: If we can get the answer every time we go to each position, then the complexity is low, so we can think that if there is a high immediately followed by a relatively short, it can be calculated, but we have to make sure that the right side can also be loaded, so we first find the highest one, Then divided into the left and right side of the calculation, and one more Curmax can follow the previous thinking calculation

Class Solution {public:    int trap (int a[], int n) {int ans = 0;int Maxindex = 0;for (int i = 1; i < n; i++) if (A[i] > A[maxindex]) maxindex = I;int Curmax = a[0];for (int i = 1; i < Maxindex; i++) {if (A[i] > Curmax) Curmax = A[i] ; else ans + = curmax-a[i];} Curmax = a[n-1];for (int i = n-2; i > maxindex; i--) {if (A[i] > Curmax) Curmax = a[i];else ans + = curmax-a[i];} return ans;    };

Leetcode trapping Rain Water