Snapchat- Group Record using Union-find

 1 1.首先ufMap里面存<Record, Record>，初始化把所有entry过一遍，都存入，使它最初的root节点都是它自己
 2 
 3 2. find部分。
 4 
 5 　　1）首先找到这个record的root节点
 6 
 7 　　2）然后把从这个record开始直到root节点所有的节点的root节点都更新成root
 8 
 9 　　3）返回root
10 
11 3. union部分，没什么特别的
12 
13 　　1）对record1,record2找到root1,root2
14 
15 　　2）如果root1 != root2，那么就设置其中一个是另外一个的root节点

 1 1.建立一个nameMap<nameString, Record>和一个numMap<number, Record>
 2 
 3 2.对于所有entry走一遍，
 4 
 5 　　1) 如果nameMap里面已经存在当前entry的name，那么就说明要union；否则就把[nameString, entry]加入map
 6 
 7 　　2）如果numMap里面已经存在当前entry的number，那么就说明要union；否则就把[number, entry]加入map
 8 3. 所以此刻ufMap里面已经有已经对于name和number group之后的结果，现在就需要把结果保存下来。
 9 
10 　　所以可以先建一个Map<String, List<Record>>整理好，再根据这个map得到List<List<Record>>

 1 public class GroupRecord {
 2     static class Record {
 3         String name;
 4         int number;
 5         public Record(String name, int number) {
 6             this.name = name;
 7             this.number = number;
 8         }
 9         
10         public String toString() {
11             return "(" + name + "," + number + ")";
12         }
13     }
14     
15     public static List<List<Record>> group(List<Record> records) {
16         Map<Record, Record> ufMap = new HashMap<Record, Record>();
17         Map<String, Record> nameMap = new HashMap<>();
18         Map<Integer, Record> numMap = new HashMap<>();
19         for(Record entry: records) {
20             ufMap.put(entry, entry);
21         }
22         for(Record entry: records) {
23             if(nameMap.containsKey(entry.name)) {
24                 union(ufMap, entry, nameMap.get(entry.name));
25             } else {
26                 nameMap.put(entry.name, entry);
27             }
28             if(numMap.containsKey(entry.number)) {
29                 union(ufMap, entry, numMap.get(entry.number));
30             } else {
31                 numMap.put(entry.number, entry);
32             }
33         }
34         Map<String, List<Record>> groupMap = new HashMap<>();
35         for(Record entry: records) {
36             Record root = find(ufMap, entry);
37             List<Record> list = groupMap.get(root.name);
38             if(list == null) {
39                 list = new ArrayList<Record>();
40             }
41             list.add(entry);
42             groupMap.put(root.name, list);
43         }
44         List<List<Record>> res = new ArrayList<List<Record>>(groupMap.values());
45         return res;
46     }
47     
48     private static Record find(Map<Record, Record> ufMap, Record record) {
49         Record root = record;
50         while(!ufMap.get(root).equals(root)) {
51             root = ufMap.get(root);
52         }
53         Record cur = record;
54         while(!cur.equals(root)) {
55             ufMap.put(record, root);
56             cur = ufMap.get(cur);
57         }
58         return root;
59     }
60     
61     private static void union(Map<Record, Record> ufMap, Record r1, Record r2) {
62         Record root1 = find(ufMap, r1);
63         Record root2 = find(ufMap, r2);
64         if(!root1.equals(root2)) {
65             ufMap.put(root1, root2);
66         }
67     }
68 
69     public static void main(String[] args) {
70         List<List<Record>> res = new ArrayList<List<Record>>();
71         ArrayList<Record> records = new ArrayList<>();
72         records.add(new Record("ABC",123));
73         records.add(new Record("ABC",456));
74         records.add(new Record("BCD",456));
75 
76         records.add(new Record("AD",342));
77         records.add(new Record("AddD",11));
78         records.add(new Record("DFX",34));
79         records.add(new Record("AD",34));
80         records.add(new Record("AD",11));
81         
82         res = group(records);
83         System.out.println(res);
84     }
85 }