[LeetCode Sync] Runtime - 167 ms (50.55%), Memory - 101.9 MB (93.93%)

Author: NamVr

0380-insert-delete-getrandom-o1/README.md

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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&#39;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&nbsp;<strong>average</strong>&nbsp;<code>O(1)</code>&nbsp;time complexity.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input</strong>
+[&quot;RandomizedSet&quot;, &quot;insert&quot;, &quot;remove&quot;, &quot;insert&quot;, &quot;getRandom&quot;, &quot;remove&quot;, &quot;insert&quot;, &quot;getRandom&quot;]
+[[], [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>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>-2<sup>31</sup> &lt;= val &lt;= 2<sup>31</sup> - 1</code></li>
+	<li>At most <code>2 *&nbsp;</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>

0380-insert-delete-getrandom-o1/solution.cpp

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+class RandomizedSet {
+public:
+    unordered_map<int,int> mp;
+    vector<int> l;
+
+    RandomizedSet() {}
+    
+    bool insert(int val) {
+        bool res = mp.find(val) == mp.end();
+        if (res) {
+            mp[val] = l.size();
+            l.push_back(val);
+        }
+        return res;
+    }
+    
+    bool remove(int val) {
+        bool res = mp.find(val) != mp.end();
+        if (res) {
+            int idx = mp[val];
+            int lastVal = l.back();
+            l[idx] = lastVal;
+            l.pop_back();
+            mp[lastVal] = idx;
+            mp.erase(val);
+        }
+        return res;
+    }
+    
+    int getRandom() {
+        return l[rand() % l.size()];
+    }
+};
+
+/**
+ * Your RandomizedSet object will be instantiated and called as such:
+ * RandomizedSet* obj = new RandomizedSet();
+ * bool param_1 = obj->insert(val);
+ * bool param_2 = obj->remove(val);
+ * int param_3 = obj->getRandom();
+ */