Insert Delete GetRandom O(1)

Insert Delete GetRandom O(1) is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Design Patterns pattern, in the Design (General/Specific) subpattern.

Problem statement

Implement the RandomizedSet class:

- RandomizedSet() Initializes the RandomizedSet object.

- bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise.

- bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise.

- int getRandom() 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 same probability of being returned.

You must implement the functions of the class such that each function works in average O(1) time complexity.

Example 1:

Input ["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"] [[], [1], [2], [2], [], [1], [2], []] Output [null, true, false, true, 2, true, false, 2]

Explanation 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.

Constraints:

- -231 <= val <= 231 - 1

- At most 2 105 calls will be made to insert, remove, and getRandom.

- There will be at least one element in the data structure when getRandom is called.

Topics and companies

Topics: Array, Hash Table, Math, Design, Randomized.

Reported in interviews at Amazon, Bloomberg, Facebook, Twitter, Microsoft, Oracle, Affirm, Yandex, Two Sigma, HRT, LinkedIn, Nvidia and others.

How to practise Insert Delete GetRandom O(1) on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(1) average for each operation (insert, remove, getRandom). All operations use hash map and vector operations that are O(1) on average. time and O(N), where N is the number of elements in the set. We store each element in a vector and a hash map. space.

Open Insert Delete GetRandom O(1) in the code editor, or read the Insert Delete GetRandom O(1) editorial for a worked solution with its approach and complexity analysis.

Where Insert Delete GetRandom O(1) sits in the DSA pattern sheet

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