LeetCode 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"   

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

Approach 2: TreeMap

  Map<String, TreeMap<Integer, String>> M;

  public TimeMap() {

    M = new HashMap<>();

  }

  public void set(String key, String value, int timestamp) {

    if (!M.containsKey(key))

      M.put(key, new TreeMap<>());

    M.get(key).put(timestamp, value);

  }

  public String get(String key, int timestamp) {

    if (!M.containsKey(key))

      return "";

    TreeMap<Integer, String> tree = M.get(key);

    Integer t = tree.floorKey(timestamp);

    return t != null ? tree.get(t) : "";

  }

Approach 1: HashMap + Binary Search

  Map<String, List<Pair<Integer, String>>> M;

  public TimeMap() {

    M = new HashMap();

  }

  public void set(String key, String value, int timestamp) {

    if (!M.containsKey(key))

      M.put(key, new ArrayList<Pair<Integer, String>>());

    M.get(key).add(new Pair(timestamp, value));

  }

  public String get(String key, int timestamp) {

    if (!M.containsKey(key))

      return "";

    List<Pair<Integer, String>> A = M.get(key);

    int i = Collections.binarySearch(A, new Pair<Integer, String>(timestamp, "{"),

        (a, b) -> Integer.compare(a.getKey(), b.getKey()));

    if (i >= 0)

      return A.get(i).getValue();

    else if (i == -1)

      return "";

    else

      return A.get(-i - 2).getValue();

  }