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insert-delete-getrandom-o1.html
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<p>Implement the <code>RandomizedSet</code> class:</p>
<ul>
<li><code>RandomizedSet()</code> Initializes the <code>RandomizedSet</code> object.</li>
<li><code>bool insert(int val)</code> Inserts an item <code>val</code> into the set if not present. Returns <code>true</code> if the item was not present, <code>false</code> otherwise.</li>
<li><code>bool remove(int val)</code> Removes an item <code>val</code> from the set if present. Returns <code>true</code> if the item was present, <code>false</code> otherwise.</li>
<li><code>int getRandom()</code> Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the <b>same probability</b> of being returned.</li>
</ul>
<p>You must implement the functions of the class such that each function works in <strong>average</strong> <code>O(1)</code> time complexity.</p>
<p> </p>
<p><strong>Example 1:</strong></p>
<pre>
<strong>Input</strong>
["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
[[], [1], [2], [2], [], [1], [2], []]
<strong>Output</strong>
[null, true, false, true, 2, true, false, 2]
<strong>Explanation</strong>
RandomizedSet randomizedSet = new RandomizedSet();
randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2].
randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2].
randomizedSet.insert(2); // 2 was already in the set, so return false.
randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.
</pre>
<p> </p>
<p><strong>Constraints:</strong></p>
<ul>
<li><code>-2<sup>31</sup> <= val <= 2<sup>31</sup> - 1</code></li>
<li>At most <code>2 * </code><code>10<sup>5</sup></code> calls will be made to <code>insert</code>, <code>remove</code>, and <code>getRandom</code>.</li>
<li>There will be <strong>at least one</strong> element in the data structure when <code>getRandom</code> is called.</li>
</ul>