Introduction

In this blog post, we will explore how to solve the LeetCode problem "380" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

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.

Explanation

• Use a dynamic array (list in Python) and a hash map (dictionary in Python): The list stores the elements of the set, allowing for O(1) random access. The hash map stores the value and its index in the list, enabling O(1) insertion and removal by index swapping.
  • Efficient Removal via Swapping: When removing an element, instead of shifting all subsequent elements in the list (which would be O(n)), swap the element to be removed with the last element in the list, then pop the last element. This maintains O(1) average time complexity for removal.
  • Handle Index Updates After Swap: When swapping elements for removal, remember to update the hash map to reflect the new index of the swapped element.

• Time Complexity: O(1) average for insert, remove, and getRandom. Space Complexity: O(n), where n is the number of elements in the set.

Code

    import random

class RandomizedSet:

    def __init__(self):
        """
        Initializes the RandomizedSet object.
        """
        self.value_list = []
        self.value_map = {}

    def insert(self, val: int) -> bool:
        """
        Inserts an item val into the set if not present.
        Returns true if the item was not present, false otherwise.
        """
        if val in self.value_map:
            return False

        self.value_list.append(val)
        self.value_map[val] = len(self.value_list) - 1
        return True

    def remove(self, val: int) -> bool:
        """
        Removes an item val from the set if present.
        Returns true if the item was present, false otherwise.
        """
        if val not in self.value_map:
            return False

        index_to_remove = self.value_map[val]
        last_element = self.value_list[-1]

        # Swap the element to be removed with the last element
        self.value_list[index_to_remove] = last_element
        self.value_list.pop()

        # Update the index of the swapped element in the hash map
        self.value_map[last_element] = index_to_remove

        # Remove the value from the hash map
        del self.value_map[val]

        return True

    def getRandom(self) -> int:
        """
        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.
        """
        return random.choice(self.value_list)


# 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()