981. Time Based Key-Value Store

Posted on Edited on In

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:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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 <= 10^7
  • All the timestamps timestamp of set are strictly increasing.
  • At most 2 * 10^5 calls will be made to set and get.

Hints/Notes

  • 2025/01/09
  • No solution from 0x3F

Solution

Language: C++

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
class TimeMap {
public:
    unordered_map<string, map<int, string>> m;

    TimeMap() {

    }

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

    string get(string key, int timestamp) {
        auto it = m[key].lower_bound(timestamp);
        if (it->first == timestamp) {
            return it->second;
        } else if (it == m[key].begin()) {
            return "";
        } else {
            return prev(it)->second;
        }
    }
};

/**
 * 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);
 */