Trapping Rain Water

完全没思路的双指针。。。。

//http://www.xuebuyuan.com/1586534.html
class Solution {
public:
int trap(vector<int>& height) {

int secHeight = 0;
int left = 0;
int right = height.size() - 1;
int area = 0;
while(left < right)
{
if(height[left] < height[right])
{
secHeight = max(height[left],secHeight);
area+= secHeight - height[left];
left++;
}
else
{
secHeight = max(height[right],secHeight);
area+= secHeight - height[right];
right--;
}

}
return area;

}
};