981. Time Based Key-Value Store

Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key’s value at a certain timestamp.

Implement the TimeMap class:

• TimeMap() Initializes the object of the data structure.
• void set(String key, String value, int timestamp) Stores the key key with the value value at the given time timestamp.
• String get(String key, int timestamp) Returns a value such that set was called previously, with timestamp_prev <= timestamp. If there are multiple such values, it returns the value associated with the largest timestamp_prev. If there are no values, it returns “”.

class TimeMap {
    HashMap<String, TreeMap<Integer, String>> map;

    /** Initialize your data structure here. */
    public TimeMap() {
        map = new HashMap();
    }
    
    public void set(String key, String value, int timestamp) {
        map.computeIfAbsent(key, k -> new TreeMap<>()).put(timestamp, value);
    }
    
    public String get(String key, int timestamp) {
        if (!map.containsKey(key)) {
            return "";
        }
        Integer time = map.get(key).floorKey(timestamp);
        if (time == null) {
            return "";
        }
        return map.get(key).get(time);
    }
}