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RandomizedSet

Certification: Advanced Level Accuracy: 100% Submissions: 2 Points: 15

Write a Python class that implements a data structure RandomizedSet supporting insert, remove, and getRandom operations 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:

      

    • Step 1: Initialize RandomizedSet.
      • 

    • Step 2: insert(1) → true, 1 added.
      • 

    • Step 3: remove(2) → false, 2 not present.
      • 

    • Step 4: insert(2) → true, 2 added.
      • 

    • Step 5: getRandom() → returns either 1 or 2.
      • 

    • Step 6: remove(1) → true, 1 removed.
      • 

    • Step 7: insert(2) → false, 2 already present.
      • 

    • Step 8: getRandom() → returns 2.
      • 

    

    •
Example 2
    

  • Input: ["RandomizedSet", "insert", "insert", "remove", "insert", "remove", "getRandom"]
[[], [1], [2], [1], [2], [2], []]
    • 

  • Output: [null, true, true, true, false, true, 1]
    • 

  • Explanation:

      

    • Step 1: Initialize RandomizedSet.
      • 

    • Step 2: insert(1) → true.
      • 

    • Step 3: insert(2) → true.
      • 

    • Step 4: remove(1) → true.
      • 

    • Step 5: insert(2) → false.
      • 

    • Step 6: remove(2) → true.
      • 

    • Step 7: getRandom() → returns 1 (set is now empty so behavior may vary).
      • 

    

    •
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
    • 

  • Time Complexity: O(1) average for all operations
    • 

  • Space Complexity: O(n) where n is the number of elements in the set
    •
ArraysHash MapTCS (Tata Consultancy Services)Goldman Sachs
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Hint
Solution

Solution Hints

    
  
  • Use a combination of a hashmap and an array
    • 
  
  • The hashmap provides O(1) lookup for checking existence and retrieving positions
    • 
  
  • The array allows O(1) random access for the getRandom operation
    • 
  
  • For efficient removal, swap the element to be removed with the last element in the array
    • 
  
  • Update the hashmap accordingly after each operation
    •

Steps to solve by this approach:

 Step 1: Create a RandomizedSet class with two data structures: an array to store values and a hashmap to map values to their indices in the array.

 Step 2: For the insert operation, check if the value already exists in the hashmap. If not, add it to the end of the array and update the hashmap with its index.

 Step 3: For the remove operation, check if the value exists in the hashmap. If it does, get its index, swap it with the last element in the array, update the hashmap for the swapped element, and then remove the last element from the array and the target value from the hashmap.

 Step 4: For the getRandom operation, use a random number generator to select a random index from the array and return the value at that index.

 Step 5: Ensure all operations maintain the consistent state between the array and the hashmap for O(1) performance.

Submitted Code :