leetcode221 Maximal Square

思路：

dp。

实现：

 class Solution
 {
 public:
     int maximalSquare(vector<vector<char>>& matrix)
     {
         if (matrix.empty()) return ;
         int m = matrix.size(), n = matrix[].size();
         vector<int> dp(m, );
         int maxn = ;
         for (int i = ; i < m; i++)
         {
             dp[i] = matrix[i][] - '';
             maxn = max(maxn, dp[i]);
         }
         for (int i = ; i < n; i++)
         {
             int pre = dp[];
             dp[] = matrix[][i] - '';
             maxn = max(dp[], maxn);
             for (int j = ; j < m; j++)
             {
                 if (matrix[j][i] == '')
                 {
                     pre = min(pre, min(dp[j - ], dp[j])) + ;
                     swap(dp[j], pre);
                     maxn = max(maxn, dp[j]);
                 }
                 else dp[j] = ;
             }
         }
         return maxn * maxn;
     }
 };