Time Based Key-Value Store

Problem Statement

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 "".

Leetcode Link

Examples:

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.

Code

Python Code

class TimeMap:

    def __init__(self):
        self.s_v = {}
        self.s_t = {}

    def set(self, key: str, value: str, timestamp: int) -> None:
        self.s_v.setdefault(key, []).append(value)
        self.s_t.setdefault(key, []).append(timestamp)

    def get(self, key: str, timestamp: int) -> str:
        lo, hi = 0, len(self.s_t.get(key, [])) - 1
        mid = 0
        while lo <= hi:
            mid = lo + (hi - lo) // 2
            if self.s_t[key][mid] == timestamp: break
            elif self.s_t[key][mid] > timestamp: hi = mid - 1
            else: lo = mid + 1
        else:
            mid = lo - 1
        return self.s_v[key][mid] if mid >= 0 else ""