Leetcode 221. Maximal Square

本题用brute force超时。可以用DP，也可以不用。

dp[i][j] 代表 以(i,j)为右下角正方形的边长。

 class Solution(object):
     def maximalSquare(self, matrix):
         """
         :type matrix: List[List[str]]
         :rtype: int
         """
         if not matrix:
             return 0

         m = len(matrix)
         n = len(matrix[0])
         res = 0
         dp = [[0 for x in range(n)] for y in range(m)]

         for i in range(m):
             if matrix[i][0] == '':
                 dp[i][0] = 1
                 res = 1

         for j in range(n):
             if matrix[0][j] == '':
                 dp[0][j] = 1
                 res = 1

         for i in range(1,m):
             for j in range(1,n):
                 if matrix[i][j] == '':
                     dp[i][j]  = min(dp[i-1][j-1], min(dp[i-1][j],dp[i][j-1])) + 1
                 res = max(res, dp[i][j])

         return res * res