# Python easy-to-understand AC solution w/ comments

• class Solution(object):
def gameOfLife(self, board):
"""
:type board: List[List[int]]
:rtype: void Do not return anything, modify board in-place instead.
"""
# use two bits to represent now and before
# first bit from the tail represents before
# second bit from the tail represents now
# too judge if it previous lived, do cell&1 and
if not board: return
directions = [[1,1],[1,0],[0,1],[-1,0],[0,-1],[-1,-1],[-1,1],[1,-1]]
for i in xrange(len(board)):
for j in xrange(len(board[-1])):
live = 0
for u,v in directions:
x,y = i+u,j+v
# if living valid neighbor cell
if 0<=x<len(board) and 0<=y<len(board[-1]) and (board[x][y]&1): live += 1
if not (board[i][j]&1):
if live==3: board[i][j] = int('10',2)
else:
# previously lived cell
if live<2 or live>3:
board[i][j] = int('01',2)
else:
board[i][j] = int('11',2)
for i in xrange(len(board)):
for j in xrange(len(board[-1])):
board[i][j]>>=1

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