981. Time Based Key-Value Store 時間戳的題目

981. Time Based Key-Value Store 時間戳的題目 

Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain timestamp.

Implement the TimeMap class:

• TimeMap() Initializes the object of the data structure.
• void set(String key, String value, int timestamp) Stores the key key with the value value at the given time timestamp.
• String get(String key, int timestamp) Returns a value such that set was called previously, with timestamp_prev <= timestamp. If there are multiple such values, it returns the value associated with the largest timestamp_prev. If there are no values, it returns "".

 

Example 1:

Input
["TimeMap", "set", "get", "get", "set", "get", "get"]
[[], ["foo", "bar", 1], ["foo", 1], ["foo", 3], ["foo", "bar2", 4], ["foo", 4], ["foo", 5]]
Output
[null, null, "bar", "bar", null, "bar2", "bar2"]

Explanation
TimeMap timeMap = new TimeMap();
timeMap.set("foo", "bar", 1);  // store the key "foo" and value "bar" along with timestamp = 1.
timeMap.get("foo", 1);         // return "bar"
timeMap.get("foo", 3);         // return "bar", since there is no value corresponding to foo at timestamp 3 and timestamp 2, then the only value is at timestamp 1 is "bar".
timeMap.set("foo", "bar2", 4); // store the key "foo" and value "bar2" along with timestamp = 4.
timeMap.get("foo", 4);         // return "bar2"
timeMap.get("foo", 5);         // return "bar2"

 

Constraints:

• 1 <= key.length, value.length <= 100
• key and value consist of lowercase English letters and digits.
• 1 <= timestamp <= 107
• All the timestamps timestamp of set are strictly increasing.
• At most 2 * 105 calls will be made to set and get.

解法:

我的解法 對於每一個[key]先建立一個dictionary，dictionary map timestamp to value

意思就是字典中包含的字典

不只如此，針對每一個key，創造另一個list ，含有所有時間形成的list

之後就可以用這個list 來做binary search，因為題目特別提到 時間戳只會遞增

基本上就是 binary search on tuples。

使用bisect right python套件即可

歡迎參考底下的code

class TimeMap:

    def __init__(self):
        self.d= defaultdict(dict)
        self.key=defaultdict(list)

    def set(self, key: str, value: str, timestamp: int) -> None:
        self.d[key][timestamp]=value
        self.key[key].append(timestamp)
        
        
    def get(self, key: str, timestamp: int) -> str:
        if key not in self.d:
            return ""
        i=bisect.bisect_right(self.key[key],timestamp)
        if i!=0:
            return self.d[key][self.key[key][i-1]]
        else:
            return ""