981. Time Based Key-Value Store

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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 <= 107
  • All the timestamps timestamp of set are strictly increasing.
  • At most 2 * 105 calls will be made to set and get.

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)Bit Manipulation (Thao tác bit)String (Chuỗi)
⏱️ Thời gian O(n)
💾 Không gian O(n)

💻 Lời Giải

C++ 0981-time-based-key-value-store.cpp 
class TimeMap {
private:
    unordered_map<string, map<int, string>> mm;
    
public:
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        mm[key][timestamp] = value;
    }
    
    string get(string key, int timestamp) {
        auto it = mm[key].upper_bound(timestamp);
        if (it == mm[key].begin()) {
            return "";
        }
        it--;
        return 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);
 */