Given a 2D binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.
Example:
Input:
1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
Output: 4
用dp来记录以i,j为右下角元素时最大的matrix。状态转移方程比较trick
Solution:
class Solution(object):
def maximalSquare(self, matrix):
"""
:type matrix: List[List[str]]
:rtype: int
"""
res = 0
dp = [[0 for i in range(len(matrix[0]))] for j in range(len(matrix))]
for i in range(len(matrix)):
for j in range(len(matrix[0])):
dp[i][j] = 1 if matrix[i][j]=='1' else 0
if i>0 and j>0 and matrix[i][j]=='1':
dp[i][j] = 1 + min(dp[i-1][j-1],min(dp[i-1][j],dp[i][j-1]))
res = max(res,dp[i][j])
return res*res