【数组】42. 接雨水

题目:

 

 

解答:

 

 图解：

 

 

class Solution {
public:
    int trap(vector<int>& height) 
    {
        int ans = 0;
        stack<int> st;
        for (int i = 0; i < height.size(); i++)
        {
            while (!st.empty() && height[st.top()] < height[i])
            {
                int cur = st.top();
                st.pop();
                if (st.empty()) 
                {
                    break;
                }
                int l = st.top();
                int r = i;
                int h = min(height[r], height[l]) - height[cur];
                
                ans += (r - l - 1) * h;
            }
            st.push(i);
        }
        return ans;
    }
};