LeetCode Trapping Rain Water

题目：

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 maxH = 0;
//left[i]表示i左边最高的值，right[i]表示i右边最高的值
int *left= new int
, *right = new int
;
for (int i = 0; i < n; i++) {
maxH = max(maxH, A[i]);
left[i] = maxH;
}
maxH = 0;
for (int i = n - 1; i >= 0; i--) {
maxH = max(maxH, A[i]);
right[i] = maxH;
}
int ans = 0;
for (int i = 0; i < n; i++)
ans += (min(left[i], right[i]) - A[i]);
delete[] left;
delete[] right;
return ans;
}
};