原题链接：Leetcode 1311. 获取你好友已观看的视频

map自定义排序 参考：C++容器map可以排序吗？

static bool cmp(const pair<string,int> &a,const pair<string,int> &b)
{
     if(a.second==b.second) return a.first<b.first;
     return a.second<b.second;
}
 map<string,int> mp;
 vector<pair<string,int>> s(mp.begin(),mp.end());
 sort(s.begin(),s.end(),cmp);

DFS

class Solution {
public:
    static bool cmp(const pair<string,int> &a,const pair<string,int> &b)
    {
        if(a.second==b.second) return a.first<b.first;
        return a.second<b.second;
    }
    map<string,int> mp;
    vector<int> visit;
    void dfs(int now,int cnt,int level,vector<vector<string>>& watchedVideos, vector<vector<int>>& friends)
    {
        if(cnt==level)  return ;
        for(auto x:friends[now])
        {
            if(!visit[x] || visit[x]>cnt+1) 
            {
                visit[x]=cnt+1;
                dfs(x,cnt+1,level,watchedVideos,friends);
            }
        }
    }
    vector<string> watchedVideosByFriends(vector<vector<string>>& watchedVideos, vector<vector<int>>& friends, int id, int level) {
        int n=friends.size();
        visit.resize(n);
        visit[id]=-1;
        dfs(id,0,level,watchedVideos,friends);
        vector<string> res;
        for(int i=0;i<n;i++) 
        {
            if(visit[i]==level) 
            {
                for(auto x:watchedVideos[i]) mp[x]++;
            }
        }
        vector<pair<string,int>> s(mp.begin(),mp.end());
        sort(s.begin(),s.end(),cmp);
        for(auto x:s) res.push_back(x.first);
        return res;

    }
};

BFS

class Solution {
public:
    static bool cmp(const pair<string,int> &a,const pair<string,int> &b)
    {
        if(a.second==b.second) return a.first<b.first;
        return a.second<b.second;
    }
    map<string,int> mp;
    vector<int> visit;
    vector<string> watchedVideosByFriends(vector<vector<string>>& watchedVideos, vector<vector<int>>& friends, int id, int level) {
        int n=friends.size();
        visit.resize(n);
        queue<int> q; q.push(id);
        while(!q.empty())
        {
            int now=q.front(); q.pop();
            for(auto x:friends[now])
            {
                if((!visit[x] || visit[x]>visit[now]+1) && x!=id)
                {
                    visit[x]=visit[now]+1;
                    if(visit[x]<level) q.push(x);
                }
            }
        }
        vector<string> res;

        for(int i=0;i<n;i++) 
        {
            if(visit[i]==level) 
            {
                for(auto x:watchedVideos[i]) mp[x]++;
            }
        }
        vector<pair<string,int>> s(mp.begin(),mp.end());
        sort(s.begin(),s.end(),cmp);
        for(auto x:s) res.push_back(x.first);
        return res;

    }
};