2257_Count_Unguarded_Cells_in_the_Grid.js

/**
 * @param {number} m
 * @param {number} n
 * @param {number[][]} guards
 * @param {number[][]} walls
 * @return {number}
 */
var countUnguarded = function(m, n, guards, walls) {
    const g = Array.from({ length: m }, () => Array.from({ length: n }, () => 0));
    
    for (const [i, j] of guards) {
        g[i][j] = 2;
    }
    
    for (const [i, j] of walls) {
        g[i][j] = 2;
    }
    
    const dirs = [-1, 0, 1, 0, -1];
    
    for (const [i, j] of guards) {
        for (let k = 0; k < 4; ++k) {
            let [x, y] = [i, j];
            let [a, b] = [dirs[k], dirs[k + 1]];
            while (x + a >= 0 && x + a < m && y + b >= 0 && y + b < n && g[x + a][y + b] < 2) {
                x += a;
                y += b;
                g[x][y] = 1;
            }
        }
    }
    
    let ans = 0;
    for (const row of g) {
        for (const v of row) {
            ans += v === 0 ? 1 : 0;
        }
    }
    
    return ans;
};