total number of connected regions in a grid

grid_dfs.py

class Solution(object):

    def __init__(self, matrix, row, col):
        self.matrix = matrix
        self.row = row
        self.col = col

    def is_safe(self, i, j, visited):
        return (
                0 <= i < self.row and
                0 <= j < self.col and
                not visited[i][j] and
                self.matrix[i][j] == "1"
        )

    def dfs(self, i, j, visited):
        row_num = [-1, 0, 0,  1]
        col_num = [0, -1, 1,  0]

        visited[i][j] = True
        
        for k in range(4):
            if self.is_safe(i + row_num[k], j + col_num[k], visited):
                self.dfs(i + row_num[k], j + col_num[k], visited)

    def num_offices(self):
        visited = [[False for j in range(self.col)] for i in range(self.row)]
        count = 0
        for i in range(self.row):
            for j in range(self.col):
                if (not visited[i][j]) and (self.matrix[i][j] == "1"):
                    self.dfs(i, j, visited)
                    count += 1

        return count