Friend recommendation

Posted 2020-10-19 apanda009

返回共同好友最多的K个好友推荐input: Personreturn

Listclass person{String id;Set friends;}

 

用pq 更快些

Comparator<Map.Entry<Integer, Integer>> comp = new Comparator<Map.Entry<Integer, Integer>>() {
            public int compare(Map.Entry<Integer, Integer> entry1, Map.Entry<Integer, Integer> entry2) {
                return entry1.getValue() - entry2.getValue();
            }
        };
         
        PriorityQueue<Map.Entry<Integer, Integer>> minHeap = new PriorityQueue<Map.Entry<Integer, Integer>>(11, comp);
         
        for (Map.Entry<Integer, Integer> each : freqMap.entrySet()) {
            minHeap.offer(each);
            if (minHeap.size() > k) minHeap.pop();
        }
         
        for (int i=1; i<=k; i++) {
            res.add(minHeap.poll().getKey());
        }
        return res;

　　

 

public Person mostMutualFriend(Person p){
    Map<String, Integer> map = new HashMap<String, Integer>();
    int max = 0;
    Person res = null;
    for(Person friend : p.friends){
      for(Person ff : friend.friends){
        if(ff.id.equals(p.id))continue;   //不能推荐自己！！！！！！！！！！！
        if(Map.containsKey(ff.id)){
          map.put(ff,map.get(ff.id)+1);
          if(map.get(ff.id)+1>max)
              max = map.get(ff.id)+1;
              res = ff;
        }
        else{
        map.put(ff.id,1);
        if(1>max)
          max = 1;
          res = ff;
        }
      }
    }
    return res;
}
class Item{
  int count;
  String id;
}
//reecommend K new friends to p
public List<String> recommendKNewfriend(Person p, int k){
    Map<String,Integer> p_f = new HashMap<String,Integer>();  //potential friend
    for(Person friend : p.friends){
        for(Person x: friend.friends){
            if(x.id.equals(p.id)||p.friends.contains(x)) continue; //x is the person p knows
            map.put(x.id,map.getOrDefault(x.id,0)+1);
        }
    }

    Item x[] = new Item[p_f.size()];  //pq 也可以 min-heap
    int index = 0;
    for(String id : p_f.keySet()){
        x[index++] = new Item(p_f.get(id),id);
    }
    quickSelect(x,0,x.length-1,k);
    List<String> res = new ArrayList<String>();
    for(int i = 0; i<k;i++){
        res.add(x[i].id);
    }
    return res;
}

public void quickSelect(Item[] item, int i, int j,int k){
    int pivot = item[j].count;
    int index = i;
    for(int k = i; k<j;k++){
        if(item[k].count>pivot) swap(item,k,index++);
    }
    swap(item,j,index);
    if(index==k-1){
    return;
    }
    else if(index>k-1){
        quickSelect(item,i,index-1,k);
    }
    else{
        quickSelect(item,index+1,j,k);
    }
}