class Solution {
  public static void main(String[] args) {
    ArrayList<String> strings = new ArrayList<String>();
    strings.add("Hello, World!");
    strings.add("Welcome to CoderPad.");
    strings.add("This pad is running Java " + Runtime.version().feature());

    for (String string : strings) {
      System.out.println(string);
    }
  }
}

class Snapshot {
  
  Map<String, String> centralizedMap;
  Map<String, List<Snapshot>> snapMap;
  int snapId = 0;
  
  public Snapshot() {
    centralizedMap = new HashMap<>();
    snapMap = new HashMap<>();
  }
  
  public void put(string key, string value) {
    centralizedMap.put(key, value);
  }
  
  public void delete(string key){
    centralizedMap.remove(key);
  }
  
  public String get(string key, Snapshot snaps){
    if(snapMap.containsKey(key)) {
      for(Snapshot snap : snamMap.get(key)) {
        if(snap.snapId == snaps.snapId) {
          return snap.value;
        }
      }
      return "SnapId for this ley does not exist";     
    } else {
      return "Key Does Not Exists";
    }
  }
  
  public Snapshot takeSnapshot(){
    for(String k : centralizedMap.keySet()) {
      snapMap.putIfAbsent(k, new ArrayList<>());
      snapMap.get(k).add(new SnapShot(centralizedMap.get(k), snapId));
    }
    
    snapId++;
  }
  
  public void deleteSnapshot(Snapshot snap){
  
  }
}

class Snapshot {
  int snapId;
  String value;
  
  public Snapshot(String value, int snapId) {
    this.value = value;
    this.snapId = snapId;
  }
}