Game of Life — LeetCode 289 Python Solution

The problem

According to Wikipedia's article: "The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970." The board is made up of an m x n grid of cells, where each cell has an initial state: live (represented by a 1) or dead (represented by a 0). Each cell interacts with its eight neighbors (horizontal, vertical, diagonal) using the following four rules (taken from the above Wikipedia article): Any live cell with fewer than two live neighbors dies as if caused by under-population.

Example

Input

board = [[0,1,0],[0,0,1],[1,1,1],[0,0,0]]

Output

[[0,0,0],[1,0,1],[0,1,1],[0,1,0]]

Python solution

class Solution:
    def gameOfLife(self, board: List[List[int]]) -> None:
        m, n = len(board), len(board[0])
        for i in range(m):
            for j in range(n):
                live = -board[i][j]
                for x in range(i - 1, i + 2):
                    for y in range(j - 1, j + 2):
                        if 0 <= x < m and 0 <= y < n and board[x][y] > 0:
                            live += 1
                if board[i][j] and (live < 2 or live > 3):
                    board[i][j] = 2
                if board[i][j] == 0 and live == 3:
                    board[i][j] = -1
        for i in range(m):
            for j in range(n):
                if board[i][j] == 2:
                    board[i][j] = 0
                elif board[i][j] == -1:
                    board[i][j] = 1

Complexity

Pattern: Matrix and Grid

Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 289. Game of Life is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Matrix.

The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.

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