[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) {
int max = A[0];
int maxid = 0,sum = 0;
for(int i = 1;i < n;i ++){
if(A[maxid] < A[i])
maxid = i;
}
for(int i = 1;i < maxid;i ++){
if(A[i] >= max)
max = A[i];
else
sum += max - A[i];
}
max = A[n - 1];
for(int i = n - 2;i > maxid;i --){
if(A[i] >= max)
max = A[i];
else
sum += max - A[i];
}
return sum;
}
};

参考