Program to implement Hash Table using Open Addressing
Last Updated :
23 Jul, 2025
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:
- Insert(1, 5): Assign the pair {1, 5} at the index (1%20 =1) in the Hash Table.
- Insert(2, 15): Assign the pair {2, 15} at the index (2%20 =2) in the Hash Table.
- Insert(3, 20): Assign the pair {3, 20} at the index (3%20 =3) in the Hash Table.
- Insert(4, 7): Assign the pair {4, 7} at the index (4%20 =4) in the Hash Table.
- 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.
- 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}.
- 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 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 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
# 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
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");
}
}
}
// 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");
}
OutputValue 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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