Introduction Link to heading
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. 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 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 Link to heading
Binary Search Solution:
type TimeEntry struct {
timestamp int
value string
}
type TimeMap struct {
store map[string][]*TimeEntry
}
/** Initialize your data structure here. */
func Constructor() TimeMap {
return TimeMap{ make(map[string][]*TimeEntry) }
}
func (this *TimeMap) Set(key string, value string, timestamp int) {
this.store[key] = append(this.store[key], &TimeEntry{timestamp, value} )
}
func (this *TimeMap) Get(key string, timestamp int) string {
list := this.store[key]
n := len(list)
if n == 0 {
return ""
}
lo, hi := 0, n
for lo < hi {
mi := lo + (hi - lo) / 2
e := list[mi]
if e.timestamp == timestamp {
return e.value
} else if e.timestamp < timestamp {
lo = mi + 1
} else {
hi = mi
}
}
if lo > 0 {
return list[lo-1].value
}
return ""
}
/**
* Your TimeMap object will be instantiated and called as such:
* obj := Constructor();
* obj.Set(key,value,timestamp);
* param_2 := obj.Get(key,timestamp);
*/
Explanation Link to heading
Lets use the fact that all entries are adding with strict increasing timestamp, therefore binary search to retrieve the data fits well.