[leetcode] 981. Time Based Key-Value Store : https://leetcode.com/problems/time-based-key-value-store/

Time Based Key-Value Store.cc

class TimeMap {

private:
    unordered_map<string, map<int, string>> m; // {key, {timestamp, value}}
    
public:
    /** Initialize your data structure here. */
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        m[key][timestamp] = value;   
    }
    
    string get(string key, int timestamp) {
        unordered_map<string, map<int,string>>:: iterator f = m.find(key);
        if(f == m.end())
            return "";
        
        map<int, string>::iterator ans = (f->second).upper_bound(timestamp);
        if(ans == (f->second).begin()) 
            return "";
        else
            return prev(ans)->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);
 */