Time Based Key-Value Store
Design
, Binary Search
, TreeMap
, HashMap
Medium
Create a timebased key-value store class TimeMap
, that supports two operations.
1.set(string key, string value, int timestamp)
Stores the
key
andvalue
, along with the giventimestamp
.
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:
All key/value strings are lowercase.
All key/value strings have length in the range
[1, 100]
The
timestamps
for allTimeMap.set
operations are strictly increasing.1 <= timestamp <= 10^7
TimeMap.set
andTimeMap.get
functions will be called a total of120000
times (combined) per test case.
Analysis & Solution
HashMap + TreeMap
Time Complexity: O(1) for each
set
operation, and O(logN) for eachget
operation, where N is the number of entries in theTimeMap
.Space Complexity: O(N).
class TimeMap {
HashMap<String, TreeMap<Integer, String>> tm;
/** Initialize your data structure here. */
public TimeMap() {
tm = new HashMap<>();
}
public void set(String key, String value, int timestamp) {
if (!tm.containsKey(key)) {
tm.put(key, new TreeMap<Integer, String>());
}
tm.get(key).put(timestamp, value);
}
public String get(String key, int timestamp) {
if (!tm.containsKey(key)) {
return "";
}
TreeMap<Integer, String> tree = tm.get(key);
Integer t = tree.floorKey(timestamp);
if (t == null) {
return "";
}
return tree.get(t);
}
}
/**
* 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);
*/
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