Time Based Key-Value Store

Problem

https://leetcode.com/problems/time-based-key-value-store/

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 <= 10:sup:`7`

• All the timestamps timestamp of set are strictly increasing.

• At most 2 * 10:sup:`5` calls will be made to set and get.

Pattern

Hash Table, String, Binary Search, Design

Approaches

Binary Search

Code

from collections import defaultdict


class TimeMap:

    def __init__(self):
        self.store = defaultdict(list)

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

    def get(self, key: str, timestamp: int) -> str:
        vals = self.store[key]

        left = 0
        right = len(vals) - 1
        closest = ""

        while left <= right:
            mid = (left + right) // 2
            if vals[mid][1] == timestamp:
                return vals[mid][0]
            elif vals[mid][1] > timestamp:
                right = mid - 1
            else:
                closest = vals[mid][0]
                left = mid + 1

        return closest

Test

>>> from time_based_key_value_store__binary_search import TimeMap
>>> t = TimeMap()
>>> t.set("foo", "bar", 1)
>>> t.get("foo", 1)
'bar'
>>> t.get("foo", 3)
'bar'
>>> t.set("foo", "bar2", 4)
>>> t.get("foo", 4)
'bar2'
>>> t.get("foo", 5)
'bar2'

class time_based_key_value_store__binary_search.TimeMap

Bases: object

get(key: str, timestamp: int) → str

set(key: str, value: str, timestamp: int) → None