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Program to implement Hash Table using Open Addressing

Last Updated : 12 Feb, 2024
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The task is to design a general Hash Table data structure with Collision case handled and that supports the Insert(), Find(), and Delete() functions.

Examples:

Suppose the operations are performed on an array of pairs, {{1, 5}, {2, 15}, {3, 20}, {4, 7}}. And an array of capacity 20 is used as a Hash Table:

  1. Insert(1, 5): Assign the pair {1, 5} at the index (1%20 =1) in the Hash Table.
  2. Insert(2, 15): Assign the pair {2, 15} at the index (2%20 =2) in the Hash Table.
  3. Insert(3, 20): Assign the pair {3, 20} at the index (3%20 =3) in the Hash Table.
  4. Insert(4, 7): Assign the pair {4, 7} at the index (4%20 =4) in the Hash Table.
  5. Find(4): The key 4 is stored at the index (4%20 = 4). Therefore, print the 7 as it is the value of the key, 4, at index 4 of the Hash Table.
  6. Delete(4): The key 4 is stored at the index (4%20 = 4). After deleting Key 4, the Hash Table has keys {1, 2, 3}.
  7. Find(4): Print -1, as the key 4 does not exist in the Hash Table.

Approach: The given problem can be solved by using the modulus Hash Function and using an array of structures as Hash Table, where each array element will store the {key, value} pair to be hashed. The collision case can be handled by Linear probing, open addressing. Follow the steps below to solve the problem:

  • Define a node, structure say HashNode, to a key-value pair to be hashed.
  • Initialize an array of the pointer of type HashNode, say *arr[] to store all key-value pairs.
  • Insert(Key, Value): Insert the pair {Key, Value} in the Hash Table.
    • Initialize a HashNode variable, say temp, with value {Key, Value}.
    • Find the index where the key can be stored using the, Hash Function and then store the index in a variable say HashIndex.
    • If arr[HashIndex] is not empty or there exists another Key, then do linear probing by continuously updating the HashIndex as HashIndex =(HashIndex+1)%capacity.
    • If arr[HashIndex] is not null, then insert the given Node by assigning the address of temp to arr[HashIndex].
  • Find(Key): Finds the value of the Key in the Hash Table.
    • Find the index where the key may exist using a Hash Function and then store the index in a variable, say HashIndex.
    • If the arr[HashIndex] contains the key, Key then returns the value of it.
    • Otherwise, do linear probing by continuously updating the HashIndex as HashIndex =(HashIndex+1)%capacity. Then, if Key is found, then return the value of the Key at that HashIndex and then return true.
    • If the Key is not found, then return -1 representing not found. Otherwise, return the value of the Key.
  • Delete(Key): Deletes the Key from the Hash Table.
    • Find the index where the key may exist using a Hash Function and then store the index in a variable, say HashIndex.
    • If the arr[HashIndex] contains the key, Key then delete by assigning {-1, -1} to the arr[HashIndex] and then return true.
    • Otherwise, do linear probing by continuously updating the HashIndex as HashIndex =(HashIndex+1)%capacity. Then, if Key is found then delete the value of the Key at that HashIndex and then return true.
    • If the Key is not found, then the return is false.

Below is the implementation of the above approach:

C++ 
// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

struct HashNode {
    int key;
    int value;
};

const int capacity = 20;
int size = 0;

struct HashNode** arr;
struct HashNode* dummy;

// Function to add key value pair
void insert(int key, int V)
{

    struct HashNode* temp
        = (struct HashNode*)malloc(sizeof(struct HashNode));
    temp->key = key;
    temp->value = V;

    // Apply hash function to find
    // index for given key
    int hashIndex = key % capacity;

    // Find next free space
    while (arr[hashIndex] != NULL
           && arr[hashIndex]->key != key
           && arr[hashIndex]->key != -1) {
        hashIndex++;
        hashIndex %= capacity;
    }

    // If new node to be inserted
    // increase the current size
    if (arr[hashIndex] == NULL || arr[hashIndex]->key == -1)
        size++;

    arr[hashIndex] = temp;
}

// Function to delete a key value pair
int deleteKey(int key)
{
    // Apply hash function to find
    // index for given key
    int hashIndex = key % capacity;

    // Finding the node with given
    // key
    while (arr[hashIndex] != NULL) {
        // if node found
        if (arr[hashIndex]->key == key) {
            // Insert dummy node here
            // for further use
            arr[hashIndex] = dummy;

            // Reduce size
            size--;

            // Return the value of the key
            return 1;
        }
        hashIndex++;
        hashIndex %= capacity;
    }

    // If not found return null
    return 0;
}

// Function to search the value
// for a given key
int find(int key)
{
    // Apply hash function to find
    // index for given key
    int hashIndex = (key % capacity);

    int counter = 0;

    // Find the node with given key
    while (arr[hashIndex] != NULL) {

        int counter = 0;
        // If counter is greater than
        // capacity
        if (counter++ > capacity)
            break;

        // If node found return its
        // value
        if (arr[hashIndex]->key == key)
            return arr[hashIndex]->value;

        hashIndex++;
        hashIndex %= capacity;
    }

    // If not found return
    // -1
    return -1;
}

// Driver Code
int main()
{
    // Space allocation
    arr = (struct HashNode**)malloc(sizeof(struct HashNode*)
                                    * capacity);
    // Assign NULL initially
    for (int i = 0; i < capacity; i++)
        arr[i] = NULL;

    dummy
        = (struct HashNode*)malloc(sizeof(struct HashNode));

    dummy->key = -1;
    dummy->value = -1;

    insert(1, 5);
    insert(2, 15);
    insert(3, 20);
    insert(4, 7);
    if (find(4) != -1)
        cout << "Value of Key 4 = " << find(4) << endl;
    else
        cout << ("Key 4 does not exists\n");

    if (deleteKey(4))
        cout << ("Node value of key 4 is deleted "
                 "successfully\n");
    else {
        cout << ("Key does not exists\n");
    }

    if (find(4) != -1)
        cout << ("Value of Key 4 = %d\n", find(4));
    else
        cout << ("Key 4 does not exists\n");
}

// This code is contributed by Lovely Jain
C 
// C program for the above approach
#include <stdio.h>
#include <stdlib.h>

struct HashNode {
    int key;
    int value;
};

const int capacity = 20;
int size = 0;

struct HashNode** arr;
struct HashNode* dummy;

// Function to add key value pair
void insert(int key, int V)
{

    struct HashNode* temp
        = (struct HashNode*)malloc(sizeof(struct HashNode));
    temp->key = key;
    temp->value = V;

    // Apply hash function to find
    // index for given key
    int hashIndex = key % capacity;

    // Find next free space
    while (arr[hashIndex] != NULL
           && arr[hashIndex]->key != key
           && arr[hashIndex]->key != -1) {
        hashIndex++;
        hashIndex %= capacity;
    }

    // If new node to be inserted
    // increase the current size
    if (arr[hashIndex] == NULL
        || arr[hashIndex]->key == -1)
        size++;

    arr[hashIndex] = temp;
}

// Function to delete a key value pair
int delete (int key)
{
    // Apply hash function to find
    // index for given key
    int hashIndex = key % capacity;

    // Finding the node with given
    // key
    while (arr[hashIndex] != NULL) {
        // if node found
        if (arr[hashIndex]->key == key) {
            // Insert dummy node here
            // for further use
            arr[hashIndex] = dummy;

            // Reduce size
            size--;

            // Return the value of the key
            return 1;
        }
        hashIndex++;
        hashIndex %= capacity;
    }

    // If not found return null
    return 0;
}

// Function to search the value
// for a given key
int find(int key)
{
    // Apply hash function to find
    // index for given key
    int hashIndex = (key % capacity);

    int counter = 0;

    // Find the node with given key
    while (arr[hashIndex] != NULL) {

        int counter = 0;
        // If counter is greater than
        // capacity
        if (counter++ > capacity)
            break;

        // If node found return its
        // value
        if (arr[hashIndex]->key == key)
            return arr[hashIndex]->value;

        hashIndex++;
        hashIndex %= capacity;
    }

    // If not found return
    // -1
    return -1;
}

// Driver Code
int main()
{
    // Space allocation
    arr = (struct HashNode**)malloc(sizeof(struct HashNode*)
                                    * capacity);
    // Assign NULL initially
    for (int i = 0; i < capacity; i++)
        arr[i] = NULL;

    dummy
        = (struct HashNode*)malloc(sizeof(struct HashNode));

    dummy->key = -1;
    dummy->value = -1;

    insert(1, 5);
    insert(2, 15);
    insert(3, 20);
    insert(4, 7);

    if (find(4) != -1)
        printf("Value of Key 4 = %d\n", find(4));
    else
        printf("Key 4 does not exists\n");

    if (delete (4))
        printf("Node value of key 4 is deleted "
               "successfully\n");
    else {
        printf("Key does not exists\n");
    }

    if (find(4) != -1)
        printf("Value of Key 4 = %d\n", find(4));
    else
        printf("Key 4 does not exists\n");
}
Java 
// Java program for the above approach
class HashNode {
    int key;
    int value;
    public HashNode(int key, int value) {
        this.key = key;
        this.value = value;
    }
}

public class Main {
    static int capacity = 20;
    static int size = 0;
    static HashNode[] arr = new HashNode[capacity];
    static HashNode dummy = new HashNode(-1, -1);

    static void insert(int key, int value) {
        HashNode temp = new HashNode(key, value);
        int hashIndex = key % capacity;
        while (arr[hashIndex] != null && arr[hashIndex].key != key && arr[hashIndex].key != -1) {
            hashIndex++;
            hashIndex %= capacity;
        }
        if (arr[hashIndex] == null || arr[hashIndex].key == -1) {
            size++;
        }
        arr[hashIndex] = temp;
    }

    static int deleteKey(int key) {
        int hashIndex = key % capacity;
        while (arr[hashIndex] != null) {
            if (arr[hashIndex].key == key) {
                arr[hashIndex] = dummy;
                size--;
                return 1;
            }
            hashIndex++;
            hashIndex %= capacity;
        }
        return 0;
    }

    static int find(int key) {
        int hashIndex = key % capacity;
        int counter = 0;
        while (arr[hashIndex] != null) {
            if (counter > capacity) {
                break;
            }
            if (arr[hashIndex].key == key) {
                return arr[hashIndex].value;
            }
            hashIndex++;
            hashIndex %= capacity;
            counter++;
        }
        return -1;
    }

    public static void main(String[] args) {
        insert(1, 5);
        insert(2, 15);
        insert(3, 20);
        insert(4, 7);
        if (find(4) != -1) {
            System.out.println("Value of Key 4 = " + find(4));
        } else {
            System.out.println("Key 4 does not exists");
        }
        if (deleteKey(4) == 1) {
            System.out.println("Node value of key 4 is deleted successfully");
        } else {
            System.out.println("Key does not exists");
        }
        if (find(4) != -1) {
            System.out.println("Value of Key 4 = " + find(4));
        } else {
            System.out.println("Key 4 does not exists");
        }
    }
}

//This code is cotriuted by shivamsharma215
Python3 
# Python program for the above approach

# Struct for HashNode
class HashNode:
    def __init__(self, key: int, value: int):
        self.key = key
        self.value = value

# Constants
capacity = 20
size = 0

# Array for HashNode
arr = [None] * capacity

# Dummy node
dummy = HashNode(-1, -1)

# Function to add key value pair
def insert(key: int, value: int):
    global size
    temp = HashNode(key, value)

    # Apply hash function to find index for given key
    hash_index = key % capacity
    
    # Find next free space
    while arr[hash_index] is not None and arr[hash_index].key != key and arr[hash_index].key != -1:
        hash_index += 1
        hash_index %= capacity
    
    # If new node to be inserted increase the current size
    if arr[hash_index] is None or arr[hash_index].key == -1:
        size += 1
    
    arr[hash_index] = temp

# Function to delete a key value pair
def delete_key(key: int):
    global size
    hash_index = key % capacity

    # Finding the node with given key
    while arr[hash_index] is not None:
        # if node found
        if arr[hash_index].key == key:
            # Insert dummy node here for further use
            arr[hash_index] = dummy
            
            # Reduce size
            size -= 1
            
            # Return the value of the key
            return 1
        hash_index += 1
        hash_index %= capacity
    
    # If not found return null
    return 0

# Function to search the value for a given key
def find(key: int):
    global size
    hash_index = key % capacity
    counter = 0
    
    # Find the node with given key
    while arr[hash_index] is not None:
        if counter > capacity:
            break
        
        # If node found return its value
        if arr[hash_index].key == key:
            return arr[hash_index].value
        
        hash_index += 1
        hash_index %= capacity
        counter += 1
    
    # If not found return -1
    return -1

# Driver code
if __name__ == "__main__":
    # Space allocation
    insert(1, 5)
    insert(2, 15)
    insert(3, 20)
    insert(4, 7)
    if find(4) != -1:
        print("Value of Key 4 = ", find(4))
    else:
        print("Key 4 does not exists")
    
    if delete_key(4):
        print("Node value of key 4 is deleted successfully")
    else:
        print("Key does not exists")
    
    if find(4) != -1:
        print("Value of Key 4 = ", find(4))
    else:
        print("Key 4 does not exists")

# This code is contributed by Vikram_Shirsat
C# 
using System;

// Class for HashNode
class HashNode
{
    public int Key { get; set; }
    public int Value { get; set; }

    public HashNode(int key, int value)
    {
        Key = key;
        Value = value;
    }
}

class HashMap
{
    // Constants
    private const int Capacity = 20;
    private int size = 0;

    // Array for HashNode
    private HashNode[] arr = new HashNode[Capacity];

    // Dummy node
    private readonly HashNode dummy = new HashNode(-1, -1);

    // Function to add key value pair
    public void Insert(int key, int value)
    {
        HashNode temp = new HashNode(key, value);

        // Apply hash function to find index for given key
        int hashIndex = key % Capacity;

        // Find next free space
        while (arr[hashIndex] != null && arr[hashIndex].Key != key && arr[hashIndex].Key != -1)
        {
            hashIndex++;
            hashIndex %= Capacity;
        }

        // If new node to be inserted, increase the current size
        if (arr[hashIndex] == null || arr[hashIndex].Key == -1)
        {
            size++;
        }

        arr[hashIndex] = temp;
    }

    // Function to delete a key value pair
    public bool DeleteKey(int key)
    {
        int hashIndex = key % Capacity;

        // Finding the node with given key
        while (arr[hashIndex] != null)
        {
            // If node found
            if (arr[hashIndex].Key == key)
            {
                // Insert dummy node here for further use
                arr[hashIndex] = dummy;

                // Reduce size
                size--;

                // Return true, indicating successful deletion
                return true;
            }

            hashIndex++;
            hashIndex %= Capacity;
        }

        // If key not found, return false
        return false;
    }

    // Function to search the value for a given key
    public int Find(int key)
    {
        int hashIndex = key % Capacity;
        int counter = 0;

        // Find the node with given key
        while (arr[hashIndex] != null)
        {
            if (counter > Capacity)
            {
                break;
            }

            // If node found, return its value
            if (arr[hashIndex].Key == key)
            {
                return arr[hashIndex].Value;
            }

            hashIndex++;
            hashIndex %= Capacity;
            counter++;
        }

        // If key not found, return -1
        return -1;
    }
}

class Program
{
    // Driver code
    static void Main()
    {
        HashMap hashMap = new HashMap();

        // Space allocation
        hashMap.Insert(1, 5);
        hashMap.Insert(2, 15);
        hashMap.Insert(3, 20);
        hashMap.Insert(4, 7);

        if (hashMap.Find(4) != -1)
        {
            Console.WriteLine("Value of Key 4 = " + hashMap.Find(4));
        }
        else
        {
            Console.WriteLine("Key 4 does not exist");
        }

        if (hashMap.DeleteKey(4))
        {
            Console.WriteLine("Node value of key 4 is deleted successfully");
        }
        else
        {
            Console.WriteLine("Key does not exist");
        }

        if (hashMap.Find(4) != -1)
        {
            Console.WriteLine("Value of Key 4 = " + hashMap.Find(4));
        }
        else
        {
            Console.WriteLine("Key 4 does not exist");
        }
    }
}
JavaScript 
// Struct for HashNode
class HashNode {
  constructor(key, value) {
    this.key = key;
    this.value = value;
  }
}

// Constants
const capacity = 20;
let size = 0;

// Array for HashNode
let arr = new Array(capacity);

// Dummy node
const dummy = new HashNode(-1, -1);

// Function to add key value pair
function insert(key, value) {
  let temp = new HashNode(key, value);

  // Apply hash function to find index for given key
  let hash_index = key % capacity;

  // Find next free space
  while (arr[hash_index] !== undefined && arr[hash_index].key !== key && arr[hash_index].key !== -1) {
    hash_index++;
    hash_index %= capacity;
  }

  // If new node to be inserted increase the current size
  if (arr[hash_index] === undefined || arr[hash_index].key === -1) {
    size++;
  }

  arr[hash_index] = temp;
}

// Function to delete a key value pair
function delete_key(key) {
  let hash_index = key % capacity;

  // Finding the node with given key
  while (arr[hash_index] !== undefined) {
    // if node found
    if (arr[hash_index].key === key) {
      // Insert dummy node here for further use
      arr[hash_index] = dummy;

      // Reduce size
      size--;

      // Return the value of the key
      return 1;
    }
    hash_index++;
    hash_index %= capacity;
  }

  // If not found return null
  return 0;
}

// Function to search the value for a given key
function find(key) {
  let hash_index = key % capacity;
  let counter = 0;

  // Find the node with given key
  while (arr[hash_index] !== undefined) {
    if (counter > capacity) {
      break;
    }

    // If node found return its value
    if (arr[hash_index].key === key) {
      return arr[hash_index].value;
    }

    hash_index++;
    hash_index %= capacity;
    counter++;
  }

  // If not found return -1
  return -1;
}

// Driver code
// Space allocation
insert(1, 5);
insert(2, 15);
insert(3, 20);
insert(4, 7);

if (find(4) !== -1) {
  console.log("Value of Key 4 = ", find(4));
} else {
  console.log("Key 4 does not exist");
}

if (delete_key(4)) {
  console.log("Node value of key 4 is deleted successfully");
} else {
  console.log("Key does not exist");
}

if (find(4) !== -1) {
  console.log("Value of Key 4 = ", find(4));
} else {
  console.log("Key 4 does not exist");
}

Output
Value of Key 4 = 7
Node value of key 4 is deleted successfully
Key 4 does not exists

Time Complexity: O(capacity), for each operation
Auxiliary Space: O(capacity)


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