Implement TimeTravelingHashTable的get和insert方法

TimeTravelingHashTable.java

/*
* TimeTravelingHashTable
* insert(key, value, timestamp)
* get(key, timestamp)
* get(key) // returns value associated with key at latest time
*
* insert("k1", "v1", 10)
* get("k1") // returns "v1"
* get("k1", 11) // returns "v1"
* insert("k1", "v2", 20)
* get("k1", 15) // returns "v1" 
* get("k1", 11) // returns "v1"
* get("k1", 21)...
*/


import java.util.*;
class TimeTravelingHashTable {
. from: 1point3acres.com/bbs 
        // <key : <timestamp : value>> = <key: sorted values on timestamp> = <key : treemap>
        HashMap<String, TreeMap<Integer, String>> map = new HashMap<>();
        
        // insert <timestamp, value> into hashmap
        public void insert(String key, String value, int timestamp) {
                if(map.containsKey(key)) {
                        Map<Integer, String> values = map.get(key);
                        values.put(timestamp, value);
                } else {
                        TreeMap<Integer, String> values = new TreeMap<>();
                        values.put(timestamp, value);
                        map.put(key, values);
                }
        }

        // get the floor value on timestamp
        public String get(String key, int timestamp) {
                if(!map.containsKey(key)) return null;
                return map.get(key).floorEntry(timestamp).getValue();         
        }

        // Return the latest value on timestamp
        public String get(String key) {
                return map.get(key).lastEntry().getValue();
        }
        public static void main(String[] args) {
                TimeTravelingHashTable hashtable = new TimeTravelingHashTable(); 
                hashtable.insert("k1", "v1", 10);
                hashtable.insert("k1", "v2", 20);
                hashtable.insert("k2", "v1", 5);
                hashtable.insert("k2", "v2", 15);
                System.out.println(hashtable.get("k1"));     //  "v1" 
                System.out.println(hashtable.get("k1", 11)); //  "v1"
                System.out.println(hashtable.get("k1", 15)); //  "v1" 
                System.out.println(hashtable.get("k1", 11)); //  "v1"
                System.out.println(hashtable.get("k1", 21)); //  "v2"
                System.out.println(hashtable.get("k2", 10)); //  "v1"
                System.out.println(hashtable.get("k2", 20)); //  "v2"
        }
}