Question

981. Time Based Key-Value Store

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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

Solution 1

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)

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);
 */

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);
 */