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"]

 

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.

Rust Solution

use std::collections::HashMap;

type Pair = (i32, String);

#[derive(Default)]
struct TimeMap {
    map: HashMap<String, Vec<Pair>>,
}

impl TimeMap {
    fn new() -> Self {
        TimeMap {
            map: HashMap::new(),
        }
    }
    fn set(&mut self, key: String, value: String, timestamp: i32) {
        self.map.entry(key).or_default().push((timestamp, value));
    }
    fn get(&mut self, key: String, timestamp: i32) -> String {
        let values = self.map.entry(key).or_default();
        match values.binary_search_by_key(&timestamp, |v| v.0) {
            Ok(i) => values[i].1.to_string(),
            Err(i) => {
                if i > 0 {
                    values[i - 1].1.to_string()
                } else {
                    "".to_string()
                }
            }
        }
    }
}

#[test]
fn test() {
    let mut kv: TimeMap = TimeMap::new();
    kv.set("foo".to_string(), "bar".to_string(), 1);
    assert_eq!(kv.get("foo".to_string(), 1), "bar".to_string());
    assert_eq!(kv.get("foo".to_string(), 3), "bar".to_string());
    kv.set("foo".to_string(), "bar2".to_string(), 4);
    assert_eq!(kv.get("foo".to_string(), 4), "bar2".to_string());
    assert_eq!(kv.get("foo".to_string(), 5), "bar2".to_string());
}

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