981. Time Based Key-Value Store

package LeetCode_981

import java.util.*
import kotlin.collections.HashMap

/**
 * 981. Time Based Key-Value Store
 * https://leetcode.com/problems/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"
 * */
class TimeMap() {

    /** Initialize your data structure here. */

    /*
    * solution 1: HashMap + TreeMap, key:String, value:TreeMap, key of TreeMap is timestamp, value of TreeMap is value,
    * Time: O(logk), k is number of timestamp,
    * Space: O(n*k), n is number of key,
    * */
    val map = HashMap<String, TreeMap<Int, String>>()

    fun set(key: String, value: String, timestamp: Int) {
        if (!map.containsKey(key)) {
            map.put(key, TreeMap())
        }
        map.get(key)!!.put(timestamp, value)
    }

    fun get(key: String, timestamp: Int): String {
        //get the first one which smaller than or equal to target
        if (map.containsKey(key)) {
            val treeMap = map.get(key)
            if (treeMap != null) {
                val entry = treeMap.floorEntry(timestamp)
                if (entry != null) {
                    return entry.value
                }
            }
        }
        return ""
    }
}
/**
 * Your TimeMap object will be instantiated and called as such:
 * var obj = TimeMap()
 * obj.set(key,value,timestamp)
 * var param_2 = obj.get(key,timestamp)
 */