leetcode-problemset/leetcode-cn/problem (English)/基于时间的键值存储(English) [time-based-key-value-store].html

<p>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&#39;s value at a certain timestamp.</p>

<p>Implement the <code>TimeMap</code> class:</p>

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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input</strong>
[&quot;TimeMap&quot;, &quot;set&quot;, &quot;get&quot;, &quot;get&quot;, &quot;set&quot;, &quot;get&quot;, &quot;get&quot;]
[[], [&quot;foo&quot;, &quot;bar&quot;, 1], [&quot;foo&quot;, 1], [&quot;foo&quot;, 3], [&quot;foo&quot;, &quot;bar2&quot;, 4], [&quot;foo&quot;, 4], [&quot;foo&quot;, 5]]
<strong>Output</strong>
[null, null, &quot;bar&quot;, &quot;bar&quot;, null, &quot;bar2&quot;, &quot;bar2&quot;]

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

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= key.length, value.length &lt;= 100</code></li>
	<li><code>key</code> and <code>value</code> consist of lowercase English letters and digits.</li>
	<li><code>1 &lt;= timestamp &lt;= 10<sup>7</sup></code></li>
	<li>All the timestamps <code>timestamp</code> of <code>set</code> are strictly increasing.</li>
	<li>At most <code>2 * 10<sup>5</sup></code> calls will be made to <code>set</code> and <code>get</code>.</li>
</ul>