981. Time Based Key-Value Store

981. Time Based Key-Value Store (Medium)

Create a timebased key-value store class TimeMap, that supports two operations.

1. set(string key, string value, int timestamp)

• Stores the key and value, along with the given timestamp.

2. get(string key, int timestamp)

• Returns a value such that set(key, value, timestamp_prev) was called previously, with timestamp_prev <= timestamp.
• If there are multiple such values, it returns the one with the largest timestamp_prev.
• If there are no values, it returns the empty string ("").

 

Example 1:

Input: inputs = ["TimeMap","set","get","get","set","get","get"], inputs = [[],["foo","bar",1],["foo",1],["foo",3],["foo","bar2",4],["foo",4],["foo",5]]
Output: [null,null,"bar","bar",null,"bar2","bar2"]
Explanation:   
TimeMap kv;   
kv.set("foo", "bar", 1); // store the key "foo" and value "bar" along with timestamp = 1   
kv.get("foo", 1);  // output "bar"   
kv.get("foo", 3); // output "bar" since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 ie "bar"   
kv.set("foo", "bar2", 4);   
kv.get("foo", 4); // output "bar2"   
kv.get("foo", 5); //output "bar2"   

Example 2:

Input: inputs = ["TimeMap","set","set","get","get","get","get","get"], inputs = [[],["love","high",10],["love","low",20],["love",5],["love",10],["love",15],["love",20],["love",25]]
Output: [null,null,null,"","high","high","low","low"]

 

Note:

1. All key/value strings are lowercase.
2. All key/value strings have length in the range [1, 100]
3. The timestamps for all TimeMap.set operations are strictly increasing.
4. 1 <= timestamp <= 10^7
5. TimeMap.set and TimeMap.get functions will be called a total of 120000 times (combined) per test case.

Companies:
Google, ByteDance, Apple, Netflix, Oracle, Sumologic, Facebook, Atlassian, Microsoft, Uber, Twitter, Amazon

Related Topics:
Hash Table, Binary Search

Solution 1.

// OJ: https://leetcode.com/problems/time-based-key-value-store/
// Author: github.com/lzl124631x
// Time:
//      TimeMap: O(1)
//      set: O(logT)
//      get: O(logT)
// Space: O(N)
class TimeMap {
    unordered_map<string, map<int, string, greater<>>> m;
public:
    TimeMap() {}
    void set(string key, string value, int timestamp) {
        m[key][timestamp] = value;
    }
    string get(string key, int timestamp) {
        if (m.count(key) == 0) return "";
        auto it = m[key].lower_bound(timestamp);
        return it == m[key].end() ? "" : it->second;
    }
};