# 981. 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:**

```python
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</sup>`
    
* All the timestamps `timestamp` of `set` are strictly increasing.
    
* At most `2 * 10<sup>5</sup>` calls will be made to `set` and `get`.
    

Solution:

```python
class TimeMap:

    def __init__(self):
        self.keyStore = {}  # key : list of [val, timestamp]

    def set(self, key: str, value: str, timestamp: int) -> None:
        if key not in self.keyStore:
            self.keyStore[key] = []
        self.keyStore[key].append([value, timestamp])

    def get(self, key: str, timestamp: int) -> str:
        res, values = "", self.keyStore.get(key, [])
        l, r = 0, len(values) - 1
        while l <= r:
            m = l + ( r - l ) // 2
            if values[m][1] <= timestamp:
                res = values[m][0]
                l = m + 1
            else:
                r = m - 1
        return res
```