【leetcode】981. Time Based Key-Value Store

题目如下：

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:

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.

解题思路：我用了两个字典，一个是dic_timestamp，以timestamp为key，value作为val；第二个是dic[val] = [timestamp]，对于val相同的timestamp以升序排列的方式保存在val对应的list中。由于set操作的timestamp是递增的，所以在set的时候只需要把timestamp插入到div[val]的最后即可；对于get操作，采用二分查找的方法找出最大的小于timestamp的历史timestamp。但是二分查找的方法会timeout，后来我发现get操作的timestamp也是递增的，但是题目没有说明，所以改进代码在get操作之后删除掉小于timestamp的所有历史数据。

代码如下：

class TimeMap(object):

    def __init__(self):

        """

        Initialize your data structure here.

        """

        self.dic_timestamp = {}

        self.dic = {}

    def set(self, key, value, timestamp):

        """

        :type key: str

        :type value: str

        :type timestamp: int

        :rtype: None

        """

        self.dic[key] = self.dic.setdefault(key,[]) + [timestamp]

        self.dic_timestamp[timestamp] = value

    def get(self, key, timestamp):

        """

        :type key: str

        :type timestamp: int

        :rtype: str

        """

        import bisect

        if key not in self.dic or len(self.dic[key]) == 0 or timestamp < self.dic[key][0]:

            return ''

        elif timestamp >= self.dic[key][-1]:

            v = self.dic[key][-1]

            self.dic[key] = [self.dic[key][-1]]

            return self.dic_timestamp[v]

        v = bisect.bisect_left(self.dic[key], timestamp)

        inx = bisect.bisect_left(self.dic[key], timestamp)

        if inx == len(self.dic[key]) or timestamp != self.dic[key][inx]:

            inx -= 1

        v = self.dic[key][inx]

        self.dic[key] = self.dic[key][inx:]

        return self.dic_timestamp[v]

巴特西

【leetcode】981. Time Based Key-Value Store

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