ZombieMatrix.swift

		let test1 = [[0,1,1,0,1],
			           [0,1,0,1,0],
			           [0,0,0,0,1],
			           [0,1,0,0,0]]
		let test2=[[0]]

		print( minHours(test1))
		print(minHours(test2))
	}
	func minHours(_ matrix:[[Int]]) -> Int {
		if matrix.count == 0 {
			return -1
		}
		var grid = matrix
		var queue = [(Int,Int)]()
		var hour = 0
		let maxRow = grid.count
		let maxCol = grid[0].count
		let dx = [0,1,0,-1]
		let dy = [1,0,-1,0]

		for row in 0..<maxRow {
			for col in 0..<maxCol {
				if grid[row][col] == 1 {
					queue.append((row,col))
				}
			}
		}
		if queue.count == 0 {
			return -1
		}
		if queue.count == maxRow * maxCol {
			return -1
		}
		var newQueue = [(Int,Int)]()

		while true {
			newQueue = []
			while !queue.isEmpty {
				let pos = queue.removeFirst()
				let row = pos.0
				let col = pos.1
				if row - 1 >= 0 && grid[row - 1][col] == 0 {
					grid[row - 1][col] = 1
					newQueue.append((row - 1, col))
				}
				if row + 1 < maxRow && grid[row + 1][col] == 0 {
					grid[row + 1][col] = 1
					newQueue.append((row + 1, col))
				}
				if col - 1 >= 0 && grid[row][col - 1] == 0 {
					grid[row][col - 1] = 1
					newQueue.append((row, col - 1))
				}
				if col + 1 < maxCol && grid[row][col + 1] == 0 {
					grid[row][col + 1] = 1
					newQueue.append((row, col + 1))
				}        
			}
			if newQueue.isEmpty {
				break
			} else {
				queue = newQueue
				hour += 1
			}
		}
		return hour
	}