Link: https://leetcode.cn/problems/time-based-key-value-store/

Question

difficulty: mid
adj diff: 2

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.

这题不难。

唯一的 tricky 就是二分法，搜索。

Code

以下代码，参考了：https://leetcode.cn/problems/time-based-key-value-store/solution/gong-shui-san-xie-yi-ti-shuang-jie-ha-xi-h5et/

class Pair {
    String key;
    String value;
    int timestamp;

    public Pair (String a, String b, int c) {
        key = a;
        value = b;
        timestamp = c;
    }
}

Map<String, List<Pair>> map;

public TimeMap() {
    map = new HashMap<String, List<Pair>>();
}

public void set(String key, String value, int timestamp) {
    if (!map.containsKey(key)) {
        List<Pair> list = new ArrayList<Pair>();
        map.put(key, list);
    }
    map.get(key).add(new Pair(key, value, timestamp));
}

public String get(String key, int timestamp) {
    List<Pair> list = map.getOrDefault(key, new ArrayList<>());
    if (list.isEmpty()) return "";

    int n = list.size();
    int l = 0, r = n - 1;
    while (l < r) {
        int mid = l + r + 1 >> 1;
        if (list.get(mid).timestamp <= timestamp) {
            l = mid;
        } else {
            r = mid - 1;
        }
    }
    return list.get(r).timestamp <= timestamp ? list.get(r).value : "";
}

981. Time Based Key-Value Store

Question

Code