981. Time Based Key-Value Store

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.

class TimeMap {
public:
    /** Initialize your data structure here. */
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        mp[key][timestamp] = value;
    }
    
    string get(string key, int timestamp) {
        auto it = mp[key].upper_bound(timestamp);
        return it == mp[key].begin() ? "" : prev(it)->second;
    }
private:
    unordered_map<string, map<int, string> > mp; // key -> <timestamp, value>
};

class TimeMap {
public:
    /** Initialize your data structure here. */
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        mp[key].push_back({timestamp, value});
    }
    
    string get(string key, int timestamp) {
        auto it = upper_bound(mp[key].begin(), mp[key].end(), pair<int, string>(timestamp, ""), [](
            const pair<int, string>& a, const pair<int, string>& b) { return a.first < b.first; });
        return it == mp[key].begin() ? "" : prev(it)->second;
    }
private:
    unordered_map<string, vector<pair<int, string> > > mp; // key -> <timestamp, value>
};

class TimeMap {
public:
    /** Initialize your data structure here. */
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        mp[key].push_back({timestamp, value});
    }
    
    string get(string key, int timestamp) {
        if (!mp.count(key)) return "";
        // if (mp[key].size() == 1 && mp[key][0].first <= timestamp) return mp[key][0].second;
        int low = 0, high = mp[key].size();
        while (low < high) {
            int mid = low + (high - low) / 2;
            if (mp[key][mid].first > timestamp) high = mid;
            else low = mid + 1;
        }
        return ( (low - 1) >= 0 && (low - 1) < mp[key].size() ) ? mp[key][low - 1].second : "";
    }
private:
    unordered_map<string, vector<pair<int, string> > > mp; // key -> <timestamp, value>
};