【LeetCode热题100（51/100）】腐烂的橘子

题目地址：链接

思路： 使用BFS模拟腐烂过程，统计新鲜橘子数量，若无法全部腐烂则返回-1，否则返回最小分钟数。

/**
 * @param {number[][]} grid
 * @return {number}
 */

let dx = [0, 1, 0, -1];
let dy = [1, 0, -1, 0];
var orangesRotting = function(grid) {
    let ans = 0;
    let [n, m] = [grid.length, grid[0].length];
    let q = [];
    let freshNum = 0;
    for(let i = 0; i < n; i ++) {
        for(let j = 0; j < m; j ++) {
            if(grid[i][j] == 2) q.push([i, j, 0]);
            if(grid[i][j] == 1) freshNum ++;
        }
    }

    while(q.length) {
        let [x, y, d] = q.shift();
        for(let i = 0; i < 4; i ++) {
            let [nx, ny, nd] = [x + dx[i], y + dy[i], d + 1];
            if(0 <= nx && nx < n && 0 <= ny && ny < m && grid[nx][ny] == 1){
                ans = Math.max(ans, nd);
                freshNum --;
                grid[nx][ny] = 2;
                q.push([nx, ny, nd]);
            }
        }
    }
    return freshNum ? -1 : ans;
};