Game of Life

Problem: Game of Life

To play game of life in place, we can use extra numbers to represent future status and current status at the same time. We can use number 2 to represent a dead cell going to become a live cell and number 3 to represent a dying live cell. Thus we can do update after checking the whole map.

Code in Python:

class Solution(object):
    def gameOfLife(self, board):
        """
        :type board: List[List[int]]
        :rtype: void Do not return anything, modify board in-place instead.
        """
        rows, cols = len(board), len(board[0])
        board[:] = [[0] * cols] + board[:] + [[0] * cols]
        for i in xrange(1, rows+1):
            for j in xrange(cols):
                sum = board[i-1][j]%2 + board[i+1][j]%2
                if j > 0:
                    sum += board[i-1][j-1]%2 + board[i][j-1]%2 + board[i+1][j-1]%2
                if j < cols - 1:
                    sum += board[i-1][j+1]%2 + board[i][j+1]%2 + board[i+1][j+1]%2

                if not board[i][j] and sum == 3:
                    board[i][j] = 2
                elif board[i][j] and (sum > 3 or sum < 2):
                    board[i][j] = 3
        board[:] = board[1:rows+1]
        for i in xrange(rows):
            for j in xrange(cols):
                if board[i][j] == 2: board[i][j] = 1
                if board[i][j] == 3: board[i][j] = 0