java-leetcode题解之第1311获取已观看视频.zip

import java.util.ArrayList; import java.util.Arrays; import java.util.HashMap; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Queue; public class Solution { public List<String> watchedVideosByFriends(List<List<String>> watchedVideos, int[][] friends, int id, int level) { int len = friends.length; // 距离 id 的步数，借助队列，初值为 -1 表示还没有赋值 int[] distance = new int[len]; Arrays.fill(distance, -1); distance[id] = 0; Queue<Integer> queue = new LinkedList<>(); queue.offer(id); while (!queue.isEmpty()) { Integer top = queue.poll(); for (int friend : friends[top]) { if (distance[friend] == -1) { distance[friend] = distance[top] + 1; queue.offer(friend); } } } List<String> res = new ArrayList<>(); // 以下同「力扣」第 451 题：根据字符出现频率排序 // 存储了距离为 level 的朋友所看的电影和对应的观看次数 Map<String, Integer> vatchedTimes = new HashMap<>(); for (int i = 0; i < len; i++) { // 只关心距离为 level 的朋友所看的电影 if (distance[i] == level) { for (String video : watchedVideos.get(i)) { if (vatchedTimes.get(video) == null) { res.add(video); vatchedTimes.put(video, 0); } else { vatchedTimes.put(video, vatchedTimes.get(video) + 1); } } } } res.sort((v1, v2) -> { if (!vatchedTimes.get(v1).equals(vatchedTimes.get(v2))) { return vatchedTimes.get(v1) - vatchedTimes.get(v2); } return v1.compareTo(v2); }); return res; } public static void main(String[] args) { List<List<String>> watchedVideos = new ArrayList<>(); List<String> video1 = new ArrayList<>(); video1.add("A"); video1.add("B"); List<String> video2 = new ArrayList<>(); video2.add("C"); List<String> video3 = new ArrayList<>(); video3.add("B"); video3.add("C"); List<String> video4 = new ArrayList<>(); video4.add("D"); watchedVideos.add(video1); watchedVideos.add(video2); watchedVideos.add(video3); watchedVideos.add(video4); int[][] friends = {{1, 2}, {0, 3}, {0, 3}, {1, 2}}; int id = 0; int level = 2; Solution solution = new Solution(); List<String> res = solution.watchedVideosByFriends(watchedVideos, friends, id, level); System.out.println(res); } }