TimeBasedKeyValueStore.java

import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.PriorityQueue;

class TimeMap {
 private Map<String, String> map;
 private Map<String, PriorityQueue<Integer>> timestamps;

 public TimeMap() {
 map = new HashMap<>();
 timestamps = new HashMap<>();
 }
 
 public void set(String key, String value, int timestamp) {
 map.put(key + "at timestamp: " + timestamp, value);
 if (!timestamps.containsKey(key)) {
 timestamps.put(key, new PriorityQueue<>(Comparator.reverseOrder()));
 timestamps.get(key).add(timestamp);
 }
 else if (timestamps.containsKey(key)) {
 timestamps.get(key).add(timestamp);
 }
 }
 
 public String get(String key, int timestamp) {
 String actualKey = key + "at timestamp: " + timestamp;
 if (map.containsKey(actualKey)) {
 return map.get(actualKey);
 } 
 else {
 if (timestamps.get(key) == null) {
 return new String();
 }
 Iterator<Integer> iterator = timestamps.get(key).iterator();
 int next = -1;
 int curr = -1;
 while (iterator.hasNext()) {
 curr = iterator.next();
 if (curr < timestamp) {
 next = curr;
 return map.get(key + "at timestamp: " + next);
 }
 }
 if (next == -1) {
 return new String();
 }
 return map.get(key + "at timestamp: " + next);
 }
 }
}

/**
 * Your TimeMap object will be instantiated and called as such:
 * TimeMap obj = new TimeMap();
 * obj.set(key,value,timestamp);
 * String param_2 = obj.get(key,timestamp);
 */