981. Time Based Key-Value Store
by Botao Xiao
981. Time Based Key-Value Store
Question:
Create a timebased key-value store class TimeMap, that supports two operations.
-
set(string key, string value, int timestamp)
Stores the key and value, along with the given timestamp.
-
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 all TimeMap.set operations are strictly increasing.
- 1 <= timestamp <= 10^7
- TimeMap.set and TimeMap.get functions will be called a total of 120000 times (combined) per test case.
Solution:
- Method 1: TreeMap
```Java
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) {
TreeMap<Integer, String> treeMap = map.containsKey(key) ? map.get(key): new TreeMap<>();
treeMap.put(timestamp, value);
map.put(key, treeMap);
}
public String get(String key, int timestamp) {
if(!map.containsKey(key)) return “”;
else{
TreeMap treeMap = map.get(key);
Map.Entry<Integer, String> entry = treeMap.floorEntry(timestamp);
if(entry == null) return “”;
else return entry.getValue();
}
}
}
/**
- 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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