981 Time Based Key-Value Store 基于时间的键值存储
Description:
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:
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 <= 10^7
All the timestamps timestamp of set are strictly increasing.
At most 2 * 10^5 calls will be made to set and get.
题目描述:
设计一个基于时间的键值数据结构，该结构可以在不同时间戳存储对应同一个键的多个值，并针对特定时间戳检索键对应的值。
实现 TimeMap 类：
TimeMap() 初始化数据结构对象
void set(String key, String value, int timestamp) 存储键 key、值 value，以及给定的时间戳 timestamp。
String get(String key, int timestamp)
返回先前调用 set(key, value, timestamp_prev) 所存储的值，其中 timestamp_prev <= timestamp 。
如果有多个这样的值，则返回对应最大的 timestamp_prev 的那个值。
如果没有值，则返回空字符串（""）。
示例 :
输入：
["TimeMap", "set", "get", "get", "set", "get", "get"]
[[], ["foo", "bar", 1], ["foo", 1], ["foo", 3], ["foo", "bar2", 4], ["foo", 4], ["foo", 5]]
输出：
[null, null, "bar", "bar", null, "bar2", "bar2"]
解释：
TimeMap timeMap = new TimeMap();
timeMap.set("foo", "bar", 1); // 存储键 "foo" 和值 "bar" ，时间戳 timestamp = 1
timeMap.get("foo", 1); // 返回 "bar"
timeMap.get("foo", 3); // 返回 "bar", 因为在时间戳 3 和时间戳 2 处没有对应 "foo" 的值，所以唯一的值位于时间戳 1 处（即 "bar"） 。
timeMap.set("foo", "bar2", 4); // 存储键 "foo" 和值 "bar2" ，时间戳 timestamp = 4
timeMap.get("foo", 4); // 返回 "bar2"
timeMap.get("foo", 5); // 返回 "bar2"
提示:
1 <= key.length, value.length <= 100
key 和 value 由小写英文字母和数字组成
1 <= timestamp <= 10^7
set 操作中的时间戳 timestamp 都是严格递增的
最多调用 set 和 get 操作 2 * 10^5 次
思路:
哈希表 ➕ 二叉搜索树
用哈希表记录 key
用 map 或者 TreeMap 记录 value
时间复杂度为 O(lgn), 空间复杂度为 O(n)
代码:
C++:
class TimeMap
{
private:
unordered_map<string, map<int, string>> m;
public:
/** Initialize your data structure here. */
TimeMap() {}
void set(string key, string value, int timestamp)
{
m[key][-timestamp] = value;
}
string get(string key, int timestamp)
{
return m.find(key) == m.end() or m[key].lower_bound(-timestamp) -> first < -timestamp ? "" : m[key].lower_bound(-timestamp) -> second;
}
};
/**
* 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);
*/
Java:
class TimeMap {
private Map<String, TreeMap<Integer, String>> map = new HashMap<>();
/** Initialize your data structure here. */
public TimeMap() {
}
public void set(String key, String value, int timestamp) {
map.computeIfAbsent(key, k -> new TreeMap<>()).put(timestamp, value);
}
public String get(String key, int timestamp) {
return map.getOrDefault(key, new TreeMap<>()).floorEntry(timestamp) == null ? "" : map.get(key).floorEntry(timestamp).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);
*/
Python:
class TimeMap:
def __init__(self):
"""
Initialize your data structure here.
"""
self.data = defaultdict(list)
def set(self, key: str, value: str, timestamp: int) -> None:
self.data[key].append([timestamp, value])
def get(self, key: str, timestamp: int) -> str:
return "" if (a := bisect_right(self.data[key], [timestamp, "z" * 101])) == 0 else self.data[key][a - 1][1]
# Your TimeMap object will be instantiated and called as such:
# obj = TimeMap()
# obj.set(key,value,timestamp)
# param_2 = obj.get(key,timestamp)
