Create a timebased key-value store class TimeMap, that supports two operations.

1. set(string key, string value, int timestamp)

• Stores the key and value, along with the given timestamp.

2. get(string key, int timestamp)

• Returns a value such that set(key, value, timestamp_prev) was called previously, with timestamp_prev <= timestamp.
• If there are multiple such values, it returns the one with the largest timestamp_prev.
• If there are no values, it returns the empty string ("").

Runtime:  212 ms, faster than 55.01% of C++ online submissions for Time Based Key-Value Store.

Memory Usage:  57 MB, less than 100.00% of C++ online submissions for Time Based Key-Value Store.

class TimeMap {
private:
  unordered_map<string, map<int, string>> mp;
  vector<int> tvec;
public:
  /** Initialize your data structure here. */
  TimeMap() {}

  void set(string key, string value, int timestamp) {
    mp[key][timestamp] = value;
  }

  string get(string key, int timestamp) {
    if(!mp.count(key)) return "";
    if(mp[key].count(timestamp)) return mp[key][timestamp];
    for(auto it = mp[key].rbegin(); it != mp[key].rend(); it++) {
      if(it->first > timestamp) continue;
      else {
        return it->second;
      }
    }
    return "";
  }
};