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);
         }
     }

 }