zombie_in_matrix.py

class Solution:
	def minHour(self, rows, columns, grid):
		if not rows or not columns:
			return 0

		q = [[i,j] for i in range(rows) for j in range(columns)
				if grid[i][j]==1]

		directions=[[1,0],[-1,0],[0,1],[0,-1]]

		time = 0

		if (not q):
			return -1

		while True:
			new=[]
			for [i,j] in q:
				for d in directions:
					ni,nj=i+d[0],j+d[1]

					if(0<=ni<rows and 0<=nj<columns and grid[ni][nj]==0):
						grid[ni][nj]==1
						new.append([ni,nj])
				q=new
				if(not q):
					break
				time = time+1
		return time