TimeBasedKeyValueStore.cpp

// Source : https://leetcode.com/problems/time-based-key-value-store/
// Author : Hao Chen
// Date   : 2019-01-30

/***************************************************************************************************** 
 *
 * Create a timebased key-value store class Timeap, 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 = ["Timeap","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:   
 * Timeap 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 = ["Timeap","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:
 * 
 * 	All key/value strings are lowercase.
 * 	All key/value strings have length in the range [1, 100]
 * 	The timestamps for all Timeap.set operations are strictly increasing.
 * 	1 <= timestamp <= 107
 * 	Timeap.set and Timeap.get functions will be called a total of 120000 times (combined) per 
 * test case.
 ******************************************************************************************************/

class TimeMap {
private:
    unordered_map<string, std::set<int>> key_time;
    unordered_map<int, string> time_value;
public:
    /** Initialize your data structure here. */
    TimeMap() {
        
    }
    
    void set(string key, string value, int timestamp) {
        key_time[key].insert(timestamp);
        time_value[timestamp] = value;
    }
    
    string get(string key, int timestamp) {
        if ( key_time.find(key) == key_time.end() ) return "";
        auto it = key_time[key].lower_bound(timestamp);
        if ( *it == timestamp ) return time_value[*it];
        if ( it != key_time[key].begin() ) {
            it--;
            return time_value[*it];
        }
        return "";
    }
};


/**
 * 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);
 */