Insert Delete GetRandom O(1)

Problem Description

Implement the RandomizedSet class with the following methods:

• 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.

Code Template

class RandomizedSet:

    def __init__(self):
        pass

    def insert(self, val: int) -> bool:
        pass

    def remove(self, val: int) -> bool:
        pass

    def getRandom(self) -> int:
        pass


# Your RandomizedSet object will be instantiated and called as such:
# obj = RandomizedSet()
# param_1 = obj.insert(val)
# param_2 = obj.remove(val)
# param_3 = obj.getRandom()

Solutions

• Solution 1 - This approach uses a combination of a list and a dictionary to achieve average O(1) time complexity for insert, remove, and getRandom operations.

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