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.

解题要点：

先用dict套list的来存key和val，再用binary search来查找合适的key。

class TimeMap(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.mydict = collections.defaultdict(list)

    def set(self, key, value, timestamp):
        """
        :type key: str
        :type value: str
        :type timestamp: int
        :rtype: None
        """
        self.mydict[key].append((timestamp, value))
        

    def get(self, key, timestamp):
        """
        :type key: str
        :type timestamp: int
        :rtype: str
        """
        # print self.mydict
        if key in self.mydict:
            lst = self.mydict[key]
            l = 0
            r = len(lst) - 1
            if lst[l][0] > timestamp:
                return ""
            if lst[r][0] < timestamp:
                return lst[r][1]
            while l <= r:
                mid = l + (r - l)/2
                if lst[mid][0] == timestamp:
                    return lst[l][1]
                elif lst[mid][0] < timestamp:
                    l += 1
                else:
                    r -= 1
            # print l, lst[l][0]
            return lst[r][1]
        return ""


# Your TimeMap object will be instantiated and called as such:
# obj = TimeMap()
# obj.set(key,value,timestamp)
# param_2 = obj.get(key,timestamp)