Trapping Rain Water

Desicription

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.

fuck

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!

Solution

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class Solution {
public:
int trap(vector<int>& height) {
if(!height.size())
return 0;
int left = 0;
int right = height.size()-1;
int left_max = height[left];
int right_max = height[right];
int res = 0;
while(left <= right){
if(height[left] <= height[right]){
if(height[left] > left_max)
left_max = height[left];
else
res += left_max - height[left];
left++;
}
else{
if(height[right] > right_max)
right_max = height[right];
else
res += right_max - height[right];
right--;
}
}
return res;
}
};