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HashMap using Array

Certification: Basic Level Accuracy: 100% Submissions: 2 Points: 8
Example 1
    

  • Input:
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
    • 

  • Output:
[null, null, null, 1, -1, null, 1, null, -1]
    • 

  • Explanation:
MyHashMap hashMap = new MyHashMap();
    
hashMap.put(1, 1);          // The map is now [[1,1]]
    
hashMap.put(2, 2);          // The map is now [[1,1], [2,2]]
    
hashMap.get(1);             // return 1
    
hashMap.get(3);             // return -1 (not found)
    
hashMap.put(2, 1);          // The map is now [[1,1], [2,1]] (update the existing value)
    
hashMap.get(2);             // return 1 
    
hashMap.remove(2);          // remove the mapping for 2, The map is now [[1,1]]
    
hashMap.get(2);             // return -1 (not found)
    •
Example 2
    

  • Input:
["MyHashMap", "put", "get", "put", "put", "get", "remove", "get", "containsKey"]

    [[], [10, 20], [10], [10, 30], [20, 40], [10], [20], [20], [10]]
    • 

  • Output:
[null, null, 20, null, null, 30, null, -1, true]
    • 

  • Explanation: Various operations are performed on the hash map, and the final containsKey check returns true.
    •
Constraints
    

  • 0 ≤ key, value ≤ 10^6
    • 

  • At most 10^4 calls will be made to put, get, remove, and containsKey
    • 

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

  • Space Complexity: O(n) where n is the capacity of the hash map
    •
ArraysHash MapHCL TechnologiesKPMG
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Hint
Solution

Solution Hints

    
  
  • Use an array of linked lists or an array of array lists to implement the hash map
    • 
  
  • Each entry in the hash map should store both key and value
    • 
  
  • Implement a hash function to map keys to array indices
    • 
  
  • Handle collisions using a technique like chaining or open addressing
    • 
  
  • For updating a value, check if the key already exists
    •

Steps to solve by this approach:

 Step 1: Create a static inner class Entry to store key-value pairs.
 Step 2: Create an array of ArrayList to handle collisions using chaining.
 Step 3: Implement a hash function that maps a key to an index in the array.
 Step 4: For put operation, check if the key already exists. If it does, update the value; otherwise, add a new entry.
 Step 5: For get operation, find the key in the appropriate bucket and return its value, or -1 if not found.
 Step 6: For remove operation, find the entry in the appropriate bucket and remove it.
 Step 7: Implement containsKey by checking if get returns a value other than -1.

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