(leetcode学习)42. 接雨水

通过这个题学习一下单调栈。

class Solution {
public:
    int trap(vector<int>& height) {
        stack<int> stk;
        int res = 0, n=height.size();

        for(int i=0; i<n; i++){
            while(!stk.empty() && height[ stk.top() ] <= height[i]){
                    int midh = height[stk.top()];
                    stk.pop();
                    if(stk.empty()) continue;
                    int lh = height[stk.top()], w = i - stk.top() - 1;
                    res += (min(lh, height[i]) - midh)*w;
                }
                stk.push(i);
            }
            return res;
        }
};