Count Square Submatrices with All Ones.py

# Given a m * n matrix of ones and zeros, return how many square submatrices have all ones.

 

# Example 1:

# Input: matrix =
# [
#   [0,1,1,1],
#   [1,1,1,1],
#   [0,1,1,1]
# ]
# Output: 15
# Explanation: 
# There are 10 squares of side 1.
# There are 4 squares of side 2.
# There is  1 square of side 3.
# Total number of squares = 10 + 4 + 1 = 15.
# Example 2:

# Input: matrix = 
# [
#   [1,0,1],
#   [1,1,0],
#   [1,1,0]
# ]
# Output: 7
# Explanation: 
# There are 6 squares of side 1.  
# There is 1 square of side 2. 
# Total number of squares = 6 + 1 = 7.
 

# Constraints:

# 1 <= arr.length <= 300
# 1 <= arr[0].length <= 300
# 0 <= arr[i][j] <= 1


class Solution:
    def countSquares(self, matrix: List[List[int]]) -> int:
        m=len(matrix)
        if not m:return 0
        n=len(matrix[0])
        count=0
        for i in range(m):
            for j in range(n):
                if matrix[i][j]:
                    if i>0 and j>0:
                        matrix[i][j]+=min(matrix[i-1][j],matrix[i][j-1],matrix[i-1][j-1])
                    count+=matrix[i][j]
        return count