221. Maximal Square
https://leetcode.com/problems/maximal-square/
solution
2d动态规划, dp[i][j]以matrix[i-1][j-1]为右下底的全是1的最大square的边长
因为涉及到前面的状态,i-1和j-1来简化初始化过程
Space can be optimized as we don't need to keep the whole dp grid as we progress down the rows in matrix
class Solution:
def maximalSquare(self, matrix: List[List[str]]) -> int:
if not matrix:
return 0
m = len(matrix)
n = len(matrix[0])
dp = [[0] * (n + 1) for _ in range(m + 1)]
max_len = 0
for i in range(m):
for j in range(n):
if matrix[i][j] == '1':
# 有些tricky
dp[i+1][j+1] = min(dp[i][j], dp[i+1][j], dp[i][j+1]) + 1
if dp[i+1][j+1] > max_len:
max_len = dp[i+1][j+1]
return max_len * max_len
时间复杂度:O(mn) 空间复杂度:OnmN)
follow up
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