FB面经Prepare: Friends Recommendation

有个getFriend() API, 让你推荐你的朋友的朋友做你的朋友，当然这个新朋友不能是你原来的老朋友

package fb;

import java.util.*;

public class ReferFriends {
    public List<String> recommendation(String name) {
        List<String> res = new ArrayList<String>();
        if (name==null || name.length()==0) return res;
        
        List<String> friends = getFriends(name);
        HashSet<String> set = new HashSet<String>();
        for (String friend : friends) {
            set.add(friend);
        }
        
        HashMap<String, Integer> map = new HashMap<String, Integer>();
        ArrayList<String>[] list = new ArrayList[friends.size()+1];
        
        for (String friend : friends) {
            List<String> ffriends = getFriends(friend);
            for (String each : ffriends) {
                if (!set.contains(each) && !each.equals(name)) {
                    //map.put(each, map.getOrDefault(each, 0) + 1);
                    if (map.containsKey(each))
                        map.put(each, map.get(each)+1);
                    else map.put(each, 1);
                } 
            }
        }
        
        for (String each : map.keySet()) {
            int count = map.get(each);
            if (list[count] == null) list[count] = new ArrayList<String>();
            list[count].add(each);
        }
        
        for (int k=list.length-1; k>=0; k--) {
            if (list[k] != null) 
                res.addAll(list[k]);
        }
        return res;
        
    }
    
    public List<String> getFriends(String name) {
        HashMap<String, List<String>> map = new HashMap<String, List<String>>();
        map.put("Lily", new ArrayList<String>());
        map.put("Lucy", new ArrayList<String>());
        map.put("Hanmeimei", new ArrayList<String>());
        map.put("Jim", new ArrayList<String>());
        map.put("Lilei", new ArrayList<String>());
        map.put("Poly", new ArrayList<String>());
        map.get("Lily").add("Lilei");
        map.get("Lily").add("Poly");
        map.get("Lily").add("Hanmeimei");
        map.get("Lily").add("Jim");
        map.get("Lucy").add("Lilei");
        map.get("Lucy").add("Poly");
        map.get("Lucy").add("Hanmeimei");
        map.get("Lucy").add("Lily");
        map.get("Lilei").add("Jim");
        map.get("Lilei").add("Lucy");
        map.get("Lilei").add("UncleWang");
        map.get("Lilei").add("Hanmeimei");
        map.get("Lilei").add("Lily");
        map.get("Jim").add("Lily");
        map.get("Jim").add("Lucy");
        map.get("Jim").add("Lilei");
        map.get("Poly").add("Jim");
        map.get("Poly").add("Lilei");
        return map.get(name);
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ReferFriends sol = new ReferFriends();
        //List<String> res = sol.recommendation("Poly");
        List<String> res = sol.recommendation("Jim");
        for (String each : res) {
            System.out.println(each);
        }
    }

}