bomberman_hackerrank.js

// https://www.hackerrank.com/challenges/bomber-man/problem

// https://youtu.be/dW15c-PwsXA
const EMPTY_CELL = ".";
const BOMB_CELL  = "O";

function fillGrid(grid){
    const col_max = grid[0].length;
    return grid.fill(BOMB_CELL.repeat(col_max));
}

function iterateGrid(grid){
    let explosions = []; // storing row and col indeces
    for(let row = 0; row < grid.length; row++){
        let newRow = "";
        for(let col = 0; col < grid[row].length; col ++){
            const char = grid[row][col];
            let newChar = char;
            switch(char){
                case "0":
                    newChar = "3";
                    break;
                case "1":
                    explosions.push([row, col]);
                    break;
                case "2":
                    newChar = "1";
                    break;
                case "3":
                    newChar = "2";
            }
            newRow += newChar;
        }
        grid[row] = newRow;
    }
    // handle exploding bombs
    if(explosions.length){
        // using array as queue
        for(const [row, col] of explosions) explodeBomb(grid, row, col);
    }
    return grid;
}

function replaceCharAt(string, char, index){
    return string.slice(0,index) + char + string.slice(index + 1);
}

function explodeBomb(grid, row, col){
    const row_max = grid.length;
    const col_max = grid[0].length;
    // center
    grid[row] = replaceCharAt(grid[row], "0", col);

    // up
    if(row - 1 >= 0) grid[row - 1] = replaceCharAt(grid[row - 1], "0", col);

    // down
    if(row + 1 < row_max) grid[row + 1] = replaceCharAt(grid[row + 1], "0", col);

    // left
    if(col - 1 >= 0) grid[row] = replaceCharAt(grid[row], "0", col - 1);

    // right
    if(col + 1 < col_max) grid[row] = replaceCharAt(grid[row], "0", col + 1);
}

function formatGrid(grid, format){
    for(let row = 0; row < grid.length; row++){
        if(format === "output"){
            // replace non-0 with bombs, and 0's with empty cell
            grid[row] = grid[row].replace(/[^0]/g, BOMB_CELL).replace(/0/g,EMPTY_CELL);
        }else{
            const bomb_cell_re  = new RegExp(BOMB_CELL,"g");
            const empty_cell_re = new RegExp("\\" + EMPTY_CELL,"g");
            // replace bomb cell with 2s, and empty cells with 0s
            grid[row] = grid[row].replace(bomb_cell_re, 2).replace(empty_cell_re,0);
        }
    }
    return grid;
}

function bomberMan(n, grid) {
    if(n === 1) return grid;

    // if even, return filled grid
    if (n % 2 === 0) return fillGrid(grid);

    // using numbers (different format) to track when bombs will explode
    grid = formatGrid(grid); // O(n * m)
    grid = iterateGrid(grid); // O(n * m)

    // remove repeated cycles
    n -= 2
    n %= 4
    
    while(n){ // O(4)
        grid = iterateGrid(grid); // O(n * m)
        n--;
    }

    // reformat back to original "." and "O"
    grid = formatGrid(grid, "output"); // O(n * m)

    return grid;
}