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LeetCode 289. Game of Life (javascript solution)

cod3pineapple profile image codingpineapple ・2 min read

Description:

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.
Any live cell with two or three live neighbors lives on to the next generation.
Any live cell with more than three live neighbors dies, as if by over-population.
Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.
The next state is created by applying the above rules simultaneously to every cell in the current state, where births and deaths occur simultaneously. Given the current state of the m x n grid board, return the next state.

Solution:

Time Complexity : O(n^2)
Space Complexity: O(n^2)

var gameOfLife = function(board) {
    const newState = Array(board.length).fill(0).map(() => Array(board[0].length).fill(0))

    //Iterate over the board and populate the newState
    for(let i = 0; i < board.length; i++) {
        for(let j = 0; j < board[i].length; j++) {
           setNewState(i, j, board, newState) 
        }
    }

    //Iterate over the board again and set the board to the newState values
    for(let i = 0; i < board.length; i++) {
        for(let j = 0; j < board[i].length; j++) {
           board[i][j] = newState[i][j]
        }
    }

    //Function to set values in newState
    function setNewState(i, j, board, newState) {
        const cell = board[i][j]
        const colMax = board[i].length
        const rowMax = board.length
        let total = 0

        // look north
        if(i-1 >= 0) total += board[i-1][j]
        // look northeast
        if(i-1 >= 0 && j+1 < colMax) total += board[i-1][j+1]
        // look east
         if(j+1 < colMax) total += board[i][j+1]
        // look southeast
        if(i+1 < rowMax && j+1 < colMax) total += board[i+1][j+1]
        // look south
        if(i+1 < rowMax) total += board[i+1][j]
        // look southwest
        if(i+1 < rowMax && j-1 >= 0) total += board[i+1][j-1]
        // look west
        if(j-1 >= 0) total += board[i][j-1]
        // look northwest
        if(j-1 >= 0 && i-1 >= 0) total += board[i-1][j-1]

        // Set values in newState to 1 if it follows the provided life rules
        if(cell === 1 && total === 2 || total === 3) {
            newState[i][j] = 1
        } else if(cell === 0 && total === 3){
            newState[i][j] = 1
        }
    }
};
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Discussion (1)

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hanpari profile image
Pavel Morava

To represent the Game of life state, you may use a set storing unique coordinates.

Typically like this:

state = { (1,2), (1,3), (1,4) }
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Coincidentally, I wrote an article about this if you are interested.

Unlike arrays, sets do not tend to run out of memory when the population is growing.

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