Game of Life

'''
Logic: We are counting the neighbours of every element,
if the current element is 1 then replacing that 1 with count of neighbours
if the current element is 0 then replacing that 0 with negative of count of neighbours.
after doing above step,we are traversing the matrix again and replacing values as per the condition like
-3 means having 3 neighbours of 0:- change to 1
2 or 3 means having 2 or 3 neighbours of 1 :-change to 1
rest all conditions 0 so change other values to 0

There is one catch,If board[i][j]=1 and 0 neighbours so it will make it 0 so we will make it 1,
anyway it is going to die only but for not disturbing the counting of others,we will make it 1
as it is 1.
'''

class Solution:

    def count_neighbors(self,i,j,board):
        x = [-1, -1, -1,  0, 0,  1, 1, 1]
        y = [-1,  0,  1, -1, 1, -1, 0, 1]
        row=len(board)
        col=len(board[0])
        ans=0

        for k in range(8):
            new_i=i+x[k]
            new_j=j+y[k]
            if new_i>=0 and new_j>=0 and new_i<row and new_j<col and board[new_i][new_j]>0:
                ans+=1
        return ans

    def gameOfLife(self, board: List[List[int]]) -> None:
        #neighbours=8
        #live cell -> <2  or >3 live neighbours-> dies
        #live cell -> 2 or 3 live neighbours-> live
        #dead cell -> =3 live neighbours ->live
        #rules:
            # 1.If it is alive now then it must be positive so if now alive to dead, sign=2
            # 2.if it is dead now then it became alive,sign will be negative, sign=-1
            #this way only 1 or -1 will be alive in the updates board

        row=len(board)
        col=len(board[0])
        for i in range(row):
            for j in range(col):
                n=self.count_neighbors(i,j,board)
                if board[i][j]==1 and (n<2 or n>3):
                    board[i][j]=2 #-2 means earlier it was alive but now it dies
                if board[i][j]==0 and n==3:
                    board[i][j]=-1

        for i in range(row):
            for j in range(col):
                if abs(board[i][j])==1:
                    board[i][j]=1
                else:
                    board[i][j]=0