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 <= 100key and value consist of lowercase English letters and digits.1 <= timestamp <= 107timestamp of set are strictly increasing.2 * 105 calls will be made to set and get.class TimeMap {
public:
unordered_map <string, vector<pair<int, string>>> m;
// TimeMap() { // default constructor unnecessary
// m.clear();
// }
void set(string key, string value, int timestamp) {
m[key].push_back({timestamp, value});
// All the timestamps `timestamp` of `set` are strictly increasing.
// So no need to worry about resetting the value of a already fed timestamp
}
string get(string key, int timestamp) {
// Given Constraint: All the timestamps `timestamp` of `set` are strictly increasing.
// Hence, the vector is already sorted
auto& v = m[key];
// Given Constraint: All the timestamps `timestamp` of `set` are strictly increasing.
// Hence, the vector is already sorted
auto it = upper_bound(v.begin(), v.end(), pair<int, string>(timestamp, ""),
[](auto& a, auto& b){ return a.first<b.first;});
// upper_bound => binary search with a special comparator as lambda fx
return it==v.begin() ? "" : 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);
*/