leetcode85 Maximal Rectangle

思路：

分别按行拆分后将这一行之前的每列叠加起来，然后使用leetcode84https://www.cnblogs.com/wangyiming/p/9620942.html的思路计算。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 
 class Solution
 {
 public:
     int maximalRectangle(vector<vector<char>>& matrix)
     {
         int n = matrix.size(); if (n == ) return ;
         int m = matrix[].size(); if (m == ) return ;
         int ans = ;
         vector<int> h(m, ), l(m, ), r(m, );
         for (int i = ; i < n; i++)
         {
             for (int j = ; j < m; j++)
             {
                 h[j] = (matrix[i][j] == '' ?  : h[j] + );
             }
             stack<int> s;
             for (int j = ; j < m; j++)
             {
                 while (!s.empty() && h[s.top()] >= h[j]) s.pop();
                 l[j] = (s.empty() ?  : s.top() + );
                 s.push(j);
             }
             while (!s.empty()) s.pop();
             for (int j = m - ; j >= ; j--)
             {
                 while (!s.empty() && h[s.top()] >= h[j]) s.pop();
                 r[j] = (s.empty() ? m -  : s.top() - );
                 s.push(j);
             }
             for (int j = ; j < m; j++)
             {
                 ans = max(ans, (r[j] - l[j] + ) * h[j]);
             }
         }
         return ans;
     }
 };
 int main()
 {
     char a[][] = {{'','','','',''},
                   {'','','','',''},
                   {'','','','',''},
                   {'','','','',''}};
     // char a[][4] = {{'1','1','1','1'},
     //               {'1','1','1','1'},
     //               {'1','1','1','1'}};
     vector<vector<char>> v;
     for (int i = ; i < ; i++)
     {
         v.push_back(vector<char>(a[i], a[i] + ));
     }
     cout << Solution().maximalRectangle(v) << endl;
     return ;
 }