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"]

public class TimeMap {

    private Map<String,TreeMap<Integer,String>> map;

    /** Initialize your data structure here. */
    public TimeMap() {
        map = new HashMap<>();
    }

    public void set(String key, String value, int timestamp) {
        if(!map.containsKey(key)) {
            map.put(key,new TreeMap<>());
        }
        map.get(key).put(timestamp,value);
    }

    public String get(String key, int timestamp) {
        TreeMap<Integer,String> treeMap = map.get(key);
        if(treeMap==null) {
            return "";
        }
        
        Integer floor = treeMap.floorKey(timestamp);
        if(floor==null) {
            return "";
        }
        return treeMap.get(floor);
    }
}

/**
 * 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);
 */

class TimeMap {
    Map<String, List<Pair<Integer, String>>> hashMap;

    public TimeMap() {
        hashMap = new HashMap();
    }

    public void set(String key, String value, int timestamp) {
        if (!hashMap.containsKey(key))
            hashMap.put(key, new ArrayList<Pair<Integer, String>>());

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

    public String get(String key, int timestamp) {
        if (!hashMap.containsKey(key)) {
            return "";
        }

        List<Pair<Integer, String>> A = hashMap.get(key);
        int idx = binarySearch(A, timestamp);
        if (idx < 0) {
            return "";
        }
        return A.get(idx).getValue();
    }

    private int binarySearch(List<Pair<Integer, String>> list, int time) {
        int low = 0, high = list.size() - 1;
        while (low <= high) {
            int mid = (low + high) >> 1;
            if (list.get(mid).getKey() <= time) {
                low = mid + 1;
            } else {
                high = mid - 1;
            }
        }
        return high;
    }
}