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981. Time Based Key-Value Store

Description

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 "".

 

Example 1:

Input
["TimeMap", "set", "get", "get", "set", "get", "get"]
[[], ["foo", "bar", 1], ["foo", 1], ["foo", 3], ["foo", "bar2", 4], ["foo", 4], ["foo", 5]]
Output
[null, null, "bar", "bar", null, "bar2", "bar2"]

Explanation
TimeMap timeMap = new TimeMap();
timeMap.set("foo", "bar", 1);  // store the key "foo" and value "bar" along with timestamp = 1.
timeMap.get("foo", 1);         // return "bar"
timeMap.get("foo", 3);         // return "bar", since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 is "bar".
timeMap.set("foo", "bar2", 4); // store the key "foo" and value "bar2" along with timestamp = 4.
timeMap.get("foo", 4);         // return "bar2"
timeMap.get("foo", 5);         // return "bar2"

 

Constraints:

• 1 <= key.length, value.length <= 100
• key and value consist of lowercase English letters and digits.
• 1 <= timestamp <= 107
• All the timestamps timestamp of set are strictly increasing.
• At most 2 * 105 calls will be made to set and get.

Solutions

• Java
• C++
• Python
• Go

• class TimeMap {
      private Map<String, TreeMap<Integer, String>> ktv = new HashMap<>();
  
      public TimeMap() {
      }
  
      public void set(String key, String value, int timestamp) {
          ktv.computeIfAbsent(key, k -> new TreeMap<>()).put(timestamp, value);
      }
  
      public String get(String key, int timestamp) {
          if (!ktv.containsKey(key)) {
              return "";
          }
          var tv = ktv.get(key);
          Integer t = tv.floorKey(timestamp);
          return t == null ? "" : tv.get(t);
      }
  }
  
  /**
   * 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);
   */
  

• class TimeMap {
  public:
      TimeMap() {
      }
  
      void set(string key, string value, int timestamp) {
          ktv[key].emplace_back(timestamp, value);
      }
  
      string get(string key, int timestamp) {
          auto& pairs = ktv[key];
          pair<int, string> p = {timestamp, string({127})};
          auto i = upper_bound(pairs.begin(), pairs.end(), p);
          return i == pairs.begin() ? "" : (i - 1)->second;
      }
  
  private:
      unordered_map<string, vector<pair<int, string>>> ktv;
  };
  
  /**
   * 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);
   */
  

• class TimeMap:
      def __init__(self):
          self.ktv = defaultdict(list)
  
      def set(self, key: str, value: str, timestamp: int) -> None:
          self.ktv[key].append((timestamp, value))
  
      def get(self, key: str, timestamp: int) -> str:
          if key not in self.ktv:
              return ''
          tv = self.ktv[key]
          i = bisect_right(tv, (timestamp, chr(127)))
          return tv[i - 1][1] if i else ''
  
  
  # Your TimeMap object will be instantiated and called as such:
  # obj = TimeMap()
  # obj.set(key,value,timestamp)
  # param_2 = obj.get(key,timestamp)
  
  

• type TimeMap struct {
  	ktv map[string][]pair
  }
  
  func Constructor() TimeMap {
  	return TimeMap{map[string][]pair{} }
  }
  
  func (this *TimeMap) Set(key string, value string, timestamp int) {
  	this.ktv[key] = append(this.ktv[key], pair{timestamp, value})
  }
  
  func (this *TimeMap) Get(key string, timestamp int) string {
  	pairs := this.ktv[key]
  	i := sort.Search(len(pairs), func(i int) bool { return pairs[i].t > timestamp })
  	if i > 0 {
  		return pairs[i-1].v
  	}
  	return ""
  }
  
  type pair struct {
  	t int
  	v string
  }
  
  /**
   * Your TimeMap object will be instantiated and called as such:
   * obj := Constructor();
   * obj.Set(key,value,timestamp);
   * param_2 := obj.Get(key,timestamp);
   */
  

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