题目

题目链接：
https://www.nowcoder.com/practice/54ab9865ce7a45968b126d6968a77f34

思路

	广度优先搜索。首先找到2坐标集合，然后每次往四周为1的坐标扩展

参考答案Java

import java.util.*;public class Solution {/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可*** @param grid int整型ArrayList<ArrayList<>>* @return int整型*/public int rotApple (ArrayList<ArrayList<Integer>> grid) {//BFSint n = grid.size();int m = grid.get(0).size();Queue<Integer> q2 = new LinkedList<>();int total1 = 0; //正常的苹果个数for (int i = 0; i < n ; i++) {for (int j = 0; j < m ; j++) {if (grid.get(i).get(j) == 2) {q2.add(i * m + j);}if (grid.get(i).get(j) == 1) {total1++;}}}int[] dirx = {-1, 1, 0, 0};int[] diry = {0, 0, -1, 1};int deep = 0;int change2 = 0; //变为腐烂的苹果的个数while (!q2.isEmpty()) {int size = q2.size();for (int i = 0; i < size ; i++) {int xy = q2.poll();int x1 = xy / m; //横坐标int y1 = xy % m; //纵坐标for (int j = 0; j < 4 ; j++) {int x2 = x1 + dirx[j];int y2 = y1 + diry[j];if (x2 >= 0 && x2 < n && y2 >= 0 && y2 < m && grid.get(x2).get(y2) == 1) {q2.add(x2 * m + y2);change2++;grid.get(x2).set(y2, 2);}}}deep++;}if (change2 != total1) return -1; //正常的苹果没有全部腐烂，返回-1return deep - 1;}
}

参考答案Go

package main/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可*** @param grid int整型二维数组* @return int整型*/
func rotApple(grid [][]int) int {// BFSn := len(grid)m := len(grid[0])total1 := 0   //正常的苹果个数q2 := []int{} //切片模拟队列for i := 0; i < n; i++ {for j := 0; j < m; j++ {if grid[i][j] == 2 {q2 = append(q2, i*m+j)}if grid[i][j] == 1 {total1++}}}change2 := 0 //正常苹果变为腐烂苹果的个数deep := 0dirx := []int{-1, 1, 0, 0}diry := []int{0, 0, -1, 1}for len(q2) > 0 {size := len(q2)q2new := []int{}for i := 0; i < size; i++ {xy := q2[i]x1 := xy / m //xy对应的 横坐标y1 := xy % m //xy对应的纵坐标for j := 0; j < 4; j++ {x2 := x1 + dirx[j]y2 := y1 + diry[j]if x2 >= 0 && x2 < n && y2 >= 0 && y2 < m && grid[x2][y2] == 1 {grid[x2][y2] = 2change2++q2new = append(q2new, x2*m+y2)}}}q2 = q2newdeep++}if change2 != total1 {return -1}return deep - 1
}