- Hashing
- Linear Probing
- Basic Operations
- Search Operation
- Insert Operation
- Delete Operation
- Complete implementation
Hash Table is a data structure which stores data in an associative manner. In a hash table, data is stored in an array format, where each data value has its own unique index value. Access of data becomes very fast if we know the index of the desired data.
Thus, it becomes a data structure in which insertion and search operations are very fast irrespective of the size of the data. Hash Table uses an array as a storage medium and uses hash technique to generate an index where an element is to be inserted or is to be located from.
Hashing
Hashing is a technique to convert a range of key values into a range of indexes of an array. We're going to use modulo operator to get a range of key values. Consider an example of hash table of size 20, and the following items are to be stored. Item are in the (key,value) format.
- (1,20)
- (2,70)
- (42,80)
- (4,25)
- (12,44)
- (14,32)
- (17,11)
- (13,78)
- (37,98)
| Sr.No. | Key | Hash | Array Index |
|---|---|---|---|
| 1 | 1 | 1 % 20 = 1 | 1 |
| 2 | 2 | 2 % 20 = 2 | 2 |
| 3 | 42 | 42 % 20 = 2 | 2 |
| 4 | 4 | 4 % 20 = 4 | 4 |
| 5 | 12 | 12 % 20 = 12 | 12 |
| 6 | 14 | 14 % 20 = 14 | 14 |
| 7 | 17 | 17 % 20 = 17 | 17 |
| 8 | 13 | 13 % 20 = 13 | 13 |
| 9 | 37 | 37 % 20 = 17 | 17 |
Linear Probing
As we can see, it may happen that the hashing technique is used to create an already used index of the array. In such a case, we can search the next empty location in the array by looking into the next cell until we find an empty cell. This technique is called linear probing.
| Sr.No. | Key | Hash | Array Index | After Linear Probing, Array Index |
|---|---|---|---|---|
| 1 | 1 | 1 % 20 = 1 | 1 | 1 |
| 2 | 2 | 2 % 20 = 2 | 2 | 2 |
| 3 | 42 | 42 % 20 = 2 | 2 | 3 |
| 4 | 4 | 4 % 20 = 4 | 4 | 4 |
| 5 | 12 | 12 % 20 = 12 | 12 | 12 |
| 6 | 14 | 14 % 20 = 14 | 14 | 14 |
| 7 | 17 | 17 % 20 = 17 | 17 | 17 |
| 8 | 13 | 13 % 20 = 13 | 13 | 13 |
| 9 | 37 | 37 % 20 = 17 | 17 | 18 |
Basic Operations
Following are the basic primary operations of a hash table.
Search − Searches an element in a hash table.
Insert − Inserts an element in a hash table.
Delete − Deletes an element from a hash table.
DataItem
Define a data item having some data and key, based on which the search is to be conducted in a hash table.
See Also
PowerShell to Get a Registry Value: A Tutorial WalkthroughHow to convert JSON object to Hashtable format using PowerShell?Learn Ruby: Arrays and Hashes Cheatsheet | CodecademyC# Program to Check if Value exists in Hashtablestruct DataItem { int data; int key;};Hash Method
Define a hashing method to compute the hash code of the key of the data item.
int hashCode(int key){ return key % SIZE;}Search Operation
Whenever an element is to be searched, compute the hash code of the key passed and locate the element using that hash code as index in the array. Use linear probing to get the element ahead if the element is not found at the computed hash code.
struct DataItem *search(int key) { //get the hash int hashIndex = hashCode(key); //move in array until an empty while(hashArray[hashIndex] != NULL) { if(hashArray[hashIndex]->key == key) return hashArray[hashIndex]; //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } return NULL; }Example
Following are the implementations of this operation in various programming language −
C C++ Java Python
#include <stdio.h>#define SIZE 10 // Define the size of the hash tablestruct DataItem { int key;};struct DataItem *hashArray[SIZE]; // Define the hash table as an array of DataItem pointersint hashCode(int key) { // Return a hash value based on the key return key % SIZE;}struct DataItem *search(int key) { // get the hash int hashIndex = hashCode(key); // move in array until an empty slot is found or the key is found while (hashArray[hashIndex] != NULL) { // If the key is found, return the corresponding DataItem pointer if (hashArray[hashIndex]->key == key) return hashArray[hashIndex]; // go to the next cell ++hashIndex; // wrap around the table hashIndex %= SIZE; } // If the key is not found, return NULL return NULL;}int main() { // Initializing the hash table with some sample DataItems struct DataItem item2 = {25}; // Assuming the key is 25 struct DataItem item3 = {64}; // Assuming the key is 64 struct DataItem item4 = {22}; // Assuming the key is 22 // Calculate the hash index for each item and place them in the hash table int hashIndex2 = hashCode(item2.key); hashArray[hashIndex2] = &item2; int hashIndex3 = hashCode(item3.key); hashArray[hashIndex3] = &item3; int hashIndex4 = hashCode(item4.key); hashArray[hashIndex4] = &item4; // Call the search function to test it int keyToSearch = 64; // The key to search for in the hash table struct DataItem *result = search(keyToSearch); printf("The element to be searched: %d", keyToSearch); if (result != NULL) { printf("\nElement found"); } else { printf("\nElement not found"); } return 0;}Output
The element to be searched: 64Element found
#include <iostream>#include <unordered_map>using namespace std;#define SIZE 10 // Define the size of the hash tablestruct DataItem { int key;};unordered_map<int, DataItem*> hashMap; // Define the hash table as an unordered_mapint hashCode(int key) { // Return a hash value based on the key return key % SIZE;}DataItem* search(int key) { // get the hash int hashIndex = hashCode(key); // move in the map until an empty slot is found or the key is found while (hashMap[hashIndex] != nullptr) { // If the key is found, return the corresponding DataItem pointer if (hashMap[hashIndex]->key == key) return hashMap[hashIndex]; // go to the next cell ++hashIndex; // wrap around the table hashIndex %= SIZE; } // If the key is not found, return nullptr return nullptr;}int main() { // Initializing the hash table with some sample DataItems DataItem item2 = {25}; // Assuming the key is 25 DataItem item3 = {64}; // Assuming the key is 64 DataItem item4 = {22}; // Assuming the key is 22 // Calculate the hash index for each item and place them in the hash table int hashIndex2 = hashCode(item2.key); hashMap[hashIndex2] = &item2; int hashIndex3 = hashCode(item3.key); hashMap[hashIndex3] = &item3; int hashIndex4 = hashCode(item4.key); hashMap[hashIndex4] = &item4; // Call the search function to test it int keyToSearch = 64; // The key to search for in the hash table DataItem* result = search(keyToSearch); cout<<"The element to be searched: "<<keyToSearch; if (result != nullptr) { cout << "\nElement found"; } else { cout << "\nElement not found"; } return 0;}Output
The element to be searched: 64Element found
import java.util.HashMap;public class Main { static final int SIZE = 10; // Define the size of the hash table static class DataItem { int key; } static HashMap<Integer, DataItem> hashMap = new HashMap<>(); // Define the hash table as a HashMap static int hashCode(int key) { // Return a hash value based on the key return key % SIZE; } static DataItem search(int key) { // get the hash int hashIndex = hashCode(key); // move in map until an empty slot is found or the key is found while (hashMap.get(hashIndex) != null) { // If the key is found, return the corresponding DataItem if (hashMap.get(hashIndex).key == key) return hashMap.get(hashIndex); // go to the next cell ++hashIndex; // wrap around the table hashIndex %= SIZE; } // If the key is not found, return null return null; }public static void main(String[] args) { // Initializing the hash table with some sample DataItems DataItem item2 = new DataItem(); item2.key = 25; // Assuming the key is 25 DataItem item3 = new DataItem(); item3.key = 64; // Assuming the key is 64 DataItem item4 = new DataItem(); item4.key = 22; // Assuming the key is 22 // Calculate the hash index for each item and place them in the hash table int hashIndex2 = hashCode(item2.key); hashMap.put(hashIndex2, item2); int hashIndex3 = hashCode(item3.key); hashMap.put(hashIndex3, item3); int hashIndex4 = hashCode(item4.key); hashMap.put(hashIndex4, item4); // Call the search function to test it int keyToSearch = 64; // The key to search for in the hash table DataItem result = search(keyToSearch); System.out.print("The element to be searched: " + keyToSearch); if (result != null) { System.out.println("\nElement found"); } else { System.out.println("\nElement not found"); } }}Output
The element to be searched: 64Element found
SIZE = 10 # Define the size of the hash tableclass DataItem: def __init__(self, key): self.key = keyhashMap = {} # Define the hash table as a dictionarydef hashCode(key): # Return a hash value based on the key return key % SIZEdef search(key): # get the hash hashIndex = hashCode(key) # move in map until an empty slot is found or the key is found while hashIndex in hashMap: # If the key is found, return the corresponding DataItem if hashMap[hashIndex].key == key: return hashMap[hashIndex] # go to the next cell hashIndex = (hashIndex + 1) % SIZE # If the key is not found, return None return None# Initializing the hash table with some sample DataItemsitem2 = DataItem(25) # Assuming the key is 25item3 = DataItem(64) # Assuming the key is 64item4 = DataItem(22) # Assuming the key is 22# Calculate the hash index for each item and place them in the hash tablehashIndex2 = hashCode(item2.key)hashMap[hashIndex2] = item2hashIndex3 = hashCode(item3.key)hashMap[hashIndex3] = item3hashIndex4 = hashCode(item4.key)hashMap[hashIndex4] = item4# Call the search function to test itkeyToSearch = 64 # The key to search for in the hash tableresult = search(keyToSearch)print("The element to be searched: ", keyToSearch)if result: print("Element found")else: print("Element not found")Output
The element to be searched: 64Element found
Insert Operation
Whenever an element is to be inserted, compute the hash code of the key passed and locate the index using that hash code as an index in the array. Use linear probing for empty location, if an element is found at the computed hash code.
void insert(int key,int data) { struct DataItem *item = (struct DataItem*) malloc(sizeof(struct DataItem)); item->data = data; item->key = key; //get the hash int hashIndex = hashCode(key); //move in array until an empty or deleted cell while(hashArray[hashIndex] != NULL && hashArray[hashIndex]->key != -1) { //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } hashArray[hashIndex] = item; }Example
Following are the implementations of this operation in various programming languages −
C C++ Java Python
#include <stdio.h>#include <stdlib.h>#define SIZE 4 // Define the size of the hash tablestruct DataItem { int key;};struct DataItem *hashArray[SIZE]; // Define the hash table as an array of DataItem pointersint hashCode(int key) { // Return a hash value based on the key return key % SIZE;}void insert(int key) { // Create a new DataItem using malloc struct DataItem *newItem = (struct DataItem*)malloc(sizeof(struct DataItem)); if (newItem == NULL) { // Check if malloc fails to allocate memory fprintf(stderr, "Memory allocation error\n"); return; } newItem->key = key; // Initialize other data members if needed // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != NULL) { // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem;}int main() { // Call the insert function with different keys to populate the hash table insert(42); // Insert an item with key 42 insert(25); // Insert an item with key 25 insert(64); // Insert an item with key 64 insert(22); // Insert an item with key 22 // Output the populated hash table for (int i = 0; i < SIZE; i++) { if (hashArray[i] != NULL) { printf("Index %d: Key %d\n", i, hashArray[i]->key); } else { printf("Index %d: Empty\n", i); } } return 0;}Output
Index 0: Key 64Index 1: Key 25Index 2: Key 42Index 3: Key 22
#include <iostream>#include <vector>#define SIZE 4 // Define the size of the hash tablestruct DataItem { int key;};std::vector<DataItem*> hashArray(SIZE, nullptr); // Define the hash table as a vector of DataItem pointersint hashCode(int key){ // Return a hash value based on the key return key % SIZE;}void insert(int key){ // Create a new DataItem using new (dynamic memory allocation) DataItem *newItem = new DataItem; newItem->key = key; // Initialize other data members if needed // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != nullptr) { // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem;}int main(){ // Call the insert function with different keys to populate the hash table insert(42); // Insert an item with key 42 insert(25); // Insert an item with key 25 insert(64); // Insert an item with key 64 insert(22); // Insert an item with key 22 // Output the populated hash table for (int i = 0; i < SIZE; i++) { if (hashArray[i] != nullptr) { std::cout << "Index " << i << ": Key " << hashArray[i]->key << std::endl; } else { std::cout << "Index " << i << ": Empty" << std::endl; } } return 0;}Output
Index 0: Key 64Index 1: Key 25Index 2: Key 42Index 3: Key 22
import java.util.Arrays;public class Main { static final int SIZE = 4; // Define the size of the hash table static class DataItem { int key; } static DataItem[] hashArray = new DataItem[SIZE]; // Define the hash table as an array of DataItem pointers static int hashCode(int key) { // Return a hash value based on the key return key % SIZE; } static void insert(int key) { // Create a new DataItem DataItem newItem = new DataItem(); newItem.key = key; // Initialize other data members if needed // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != null) { // Move to the next cell hashIndex++; // Wrap around the table if needed hashIndex %= SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem; }public static void main(String[] args) { // Call the insert function with different keys to populate the hash table insert(42); // Insert an item with key 42 insert(25); // Insert an item with key 25 insert(64); // Insert an item with key 64 insert(22); // Insert an item with key 22 // Output the populated hash table for (int i = 0; i < SIZE; i++) { if (hashArray[i] != null) { System.out.println("Index " + i + ": Key " + hashArray[i].key); } else { System.out.println("Index " + i + ": Empty"); } } }}Output
Index 0: Key 64Index 1: Key 25Index 2: Key 42Index 3: Key 22
SIZE = 4 # Define the size of the hash tableclass DataItem: def __init__(self, key): self.key = keyhashArray = [None] * SIZE # Define the hash table as a list of DataItem pointersdef hashCode(key): # Return a hash value based on the key return key % SIZEdef insert(key): # Create a new DataItem newItem = DataItem(key) # Initialize other data members if needed # Calculate the hash index for the key hashIndex = hashCode(key) # Handle collisions (linear probing) while hashArray[hashIndex] is not None: # Move to the next cell hashIndex += 1 # Wrap around the table if needed hashIndex %= SIZE # Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem# Call the insert function with different keys to populate the hash tableinsert(42) # Insert an item with key 42insert(25) # Insert an item with key 25insert(64) # Insert an item with key 64insert(22) # Insert an item with key 22# Output the populated hash tablefor i in range(SIZE): if hashArray[i] is not None: print(f"Index {i}: Key {hashArray[i].key}") else: print(f"Index {i}: Empty")Output
Index 0: Key 64Index 1: Key 25Index 2: Key 42Index 3: Key 22
Delete Operation
Whenever an element is to be deleted, compute the hash code of the key passed and locate the index using that hash code as an index in the array. Use linear probing to get the element ahead if an element is not found at the computed hash code. When found, store a dummy item there to keep the performance of the hash table intact.
struct DataItem* delete(struct DataItem* item) { int key = item->key; //get the hash int hashIndex = hashCode(key); //move in array until an empty while(hashArray[hashIndex] !=NULL) { if(hashArray[hashIndex]->key == key) { struct DataItem* temp = hashArray[hashIndex]; //assign a dummy item at deleted position hashArray[hashIndex] = dummyItem; return temp; } //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } return NULL; }Example
Following are the implementations of the deletion operation for Hash Table in various programming languages −
C C++ Java Python
#include <stdio.h>#include <stdlib.h>#define SIZE 5 // Define the size of the hash tablestruct DataItem { int key;};struct DataItem *hashArray[SIZE]; // Define the hash table as an array of DataItem pointersint hashCode(int key) { // Implement your hash function here // Return a hash value based on the key}void insert(int key) { // Create a new DataItem using malloc struct DataItem *newItem = (struct DataItem*)malloc(sizeof(struct DataItem)); if (newItem == NULL) { // Check if malloc fails to allocate memory fprintf(stderr, "Memory allocation error\n"); return; } newItem->key = key; // Initialize other data members if needed // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != NULL) { // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem; // Print the inserted item's key and hash index printf("Inserted key %d at index %d\n", newItem->key, hashIndex);}void delete(int key) { // Find the item in the hash table int hashIndex = hashCode(key); while (hashArray[hashIndex] != NULL) { if (hashArray[hashIndex]->key == key) { // Mark the item as deleted (optional: free memory) free(hashArray[hashIndex]); hashArray[hashIndex] = NULL; return; } // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // If the key is not found, print a message printf("Item with key %d not found.\n", key);}int main() { // Call the insert function with different keys to populate the hash table printf("Hash Table Contents before deletion:\n"); insert(1); // Insert an item with key 42 insert(2); // Insert an item with key 25 insert(3); // Insert an item with key 64 insert(4); // Insert an item with key 22 int ele1 = 2; int ele2 = 4; printf("The key to be deleted: %d and %d", ele1, ele2); delete(ele1); // Delete an item with key 42 delete(ele2); // Delete an item with key 25 // Print the hash table's contents after delete operations printf("\nHash Table Contents after deletion:\n"); for (int i = 1; i < SIZE; i++) { if (hashArray[i] != NULL) { printf("Index %d: Key %d\n", i, hashArray[i]->key); } else { printf("Index %d: Empty\n", i); } } return 0;}Output
Hash Table Contents before deletion:Inserted key 1 at index 1Inserted key 2 at index 2Inserted key 3 at index 3Inserted key 4 at index 4The key to be deleted: 2 and 4Hash Table Contents after deletion:Index 1: Key 1Index 2: EmptyIndex 3: Key 3Index 4: Empty
#include <iostream>using namespace std;const int SIZE = 5; // Define the size of the hash tablestruct DataItem { int key;};struct DataItem* hashArray[SIZE]; // Define the hash table as an array of DataItem pointersint hashCode(int key) { // Implement your hash function here // Return a hash value based on the key // A simple hash function (modulo division) return key % SIZE;}void insert(int key) { // Create a new DataItem using new struct DataItem* newItem = new DataItem; newItem->key = key; // Initialize other data members if needed // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != nullptr) { // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = newItem; // Print the inserted item's key and hash index cout << "Inserted key " << newItem->key << " at index " << hashIndex << endl;}void deleteItem(int key) { // Find the item in the hash table int hashIndex = hashCode(key); while (hashArray[hashIndex] != nullptr) { if (hashArray[hashIndex]->key == key) { // Mark the item as deleted (optional: free memory) delete hashArray[hashIndex]; hashArray[hashIndex] = nullptr; return; } // Move to the next cell ++hashIndex; // Wrap around the table if needed hashIndex %= SIZE; } // If the key is not found, print a message cout << "Item with key " << key << " not found." << endl;}int main() { // Call the insert function with different keys to populate the hash table cout<<"Hash Table Contents before deletion:\n"; insert(1); // Insert an item with key 42 insert(2); // Insert an item with key 25 insert(3); // Insert an item with key 64 insert(4); // Insert an item with key 22 int ele1 = 2; int ele2 = 4; cout<<"The key to be deleted: "<<ele1<<" and "<<ele2<<"\n"; deleteItem(2); // Delete an item with key 42 deleteItem(4); // Delete an item with key 25 cout<<"Hash Table Contents after deletion:\n"; // Print the hash table's contents after delete operations for (int i = 1; i < SIZE; i++) { if (hashArray[i] != nullptr) { cout << "Index " << i << ": Key " << hashArray[i]->key << endl; } else { cout << "Index " << i << ": Empty" << endl; } } return 0;}Output
Hash Table Contents before deletion:Inserted key 1 at index 1Inserted key 2 at index 2Inserted key 3 at index 3Inserted key 4 at index 4The key to be deleted: 2 and 4Hash Table Contents after deletion:Index 1: Key 1Index 2: EmptyIndex 3: Key 3Index 4: Empty
public class Main { static final int SIZE = 5; // Define the size of the hash table static class DataItem { int key; DataItem(int key) { this.key = key; } } static DataItem[] hashArray = new DataItem[SIZE]; // Define the hash table as an array of DataItem objects static int hashCode(int key) { // Implement your hash function here // Return a hash value based on the key return key % SIZE; // A simple hash function using modulo operator } static void insert(int key) { // Calculate the hash index for the key int hashIndex = hashCode(key); // Handle collisions (linear probing) while (hashArray[hashIndex] != null) { // Move to the next cell hashIndex = (hashIndex + 1) % SIZE; } // Insert the new DataItem at the calculated index hashArray[hashIndex] = new DataItem(key); // Print the inserted item's key and hash index System.out.println("Inserted key " + key + " at index " + hashIndex); } static void delete(int key) { // Find the item in the hash table int hashIndex = hashCode(key); while (hashArray[hashIndex] != null) { if (hashArray[hashIndex].key == key) { // Mark the item as deleted (optional: free memory) hashArray[hashIndex] = null; // Print the deleted item's key and hash index return; } // Move to the next cell hashIndex = (hashIndex + 1) % SIZE; } // If the key is not found, print a message System.out.println("Item with key " + key + " not found."); }public static void main(String[] args) { // Call the insert function with different keys to populate the hash table System.out.println("Hash Table Contents before deletion: "); insert(1); // Insert an item with key 1 insert(2); // Insert an item with key 2 insert(3); // Insert an item with key 3 insert(4); // Insert an item with key 4 int ele1 = 2; int ele2 = 4; System.out.print("The keys to be deleted: " + ele1 + " and " + ele2); delete(ele1); // Delete an item with key 2 delete(ele2); // Delete an item with key 4 // Print the hash table's contents after delete operations System.out.println("\nHash Table Contents after deletion:"); for (int i = 1; i < SIZE; i++) { if (hashArray[i] != null) { System.out.println("Index " + i + ": Key " + hashArray[i].key); } else { System.out.println("Index " + i + ": Empty"); } } }}Output
Hash Table Contents before deletion: Inserted key 1 at index 1Inserted key 2 at index 2Inserted key 3 at index 3Inserted key 4 at index 4The keys to be deleted: 2 and 4Hash Table Contents after deletion:Index 1: Key 1Index 2: EmptyIndex 3: Key 3Index 4: Empty
SIZE = 5 # Define the size of the hash tableclass DataItem: def __init__(self, key): self.key = keydef hashCode(key): # Implement your hash function here # Return a hash value based on the key return key % SIZEdef insert(key): global hashArray # Access the global hashArray variable # Calculate the hash index for the key hashIndex = hashCode(key) # Handle collisions (linear probing) while hashArray[hashIndex] is not None: # Move to the next cell hashIndex = (hashIndex + 1) % SIZE # Insert the new DataItem at the calculated index hashArray[hashIndex] = DataItem(key) # Print the inserted item's key and hash index print(f"Inserted key {key} at index {hashIndex}")def delete(key): global hashArray # Access the global hashArray variable # Find the item in the hash table hashIndex = hashCode(key) while hashArray[hashIndex] is not None: if hashArray[hashIndex].key == key: # Mark the item as deleted (optional: free memory) hashArray[hashIndex] = None return # Move to the next cell hashIndex = (hashIndex + 1) % SIZE # If the key is not found, print a message print(f"Item with key {key} not found.")# Initialize the hash table as a list of None valueshashArray = [None] * SIZEprint("Hash Table Contents before deletion:")# Call the insert function with different keys to populate the hash tableinsert(1) # Insert an item with key 1insert(2) # Insert an item with key 2insert(3) # Insert an item with key 3insert(4) # Insert an item with key 4ele1 = 2ele2 = 4print("The keys to be deleted: ", ele1, " and ", ele2)delete(2) # Delete an item with key 2delete(4) # Delete an item with key 4# Print the hash table's contents after delete operationsprint("Hash Table Contents after deletion:")for i in range(1, SIZE): if hashArray[i] is not None: print(f"Index {i}: Key {hashArray[i].key}") else: print(f"Index {i}: Empty")Output
Hash Table Contents before deletion:Inserted key 1 at index 1Inserted key 2 at index 2Inserted key 3 at index 3Inserted key 4 at index 4The keys to be deleted: 2 and 4Hash Table Contents after deletion:Index 1: Key 1Index 2: EmptyIndex 3: Key 3Index 4: Empty
Complete implementation
Following are the complete implementations of the above operations in various programming languages −
C C++ Java Python
#include <stdio.h>#include <string.h>#include <stdlib.h>#include <stdbool.h>#define SIZE 20struct DataItem { int data; int key;};struct DataItem* hashArray[SIZE]; struct DataItem* dummyItem;struct DataItem* item;int hashCode(int key) { return key % SIZE;}struct DataItem *search(int key) { //get the hash int hashIndex = hashCode(key); //move in array until an empty while(hashArray[hashIndex] != NULL) { if(hashArray[hashIndex]->key == key) return hashArray[hashIndex]; //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } return NULL; }void insert(int key,int data) { struct DataItem *item = (struct DataItem*) malloc(sizeof(struct DataItem)); item->data = data; item->key = key; //get the hash int hashIndex = hashCode(key); //move in array until an empty or deleted cell while(hashArray[hashIndex] != NULL && hashArray[hashIndex]->key != -1) { //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } hashArray[hashIndex] = item;}struct DataItem* delete(struct DataItem* item) { int key = item->key; //get the hash int hashIndex = hashCode(key); //move in array until an empty while(hashArray[hashIndex] != NULL) { if(hashArray[hashIndex]->key == key) { struct DataItem* temp = hashArray[hashIndex]; //assign a dummy item at deleted position hashArray[hashIndex] = dummyItem; return temp; } //go to next cell ++hashIndex; //wrap around the table hashIndex %= SIZE; } return NULL; }void display() { int i = 0; for(i = 0; i<SIZE; i++) { if(hashArray[i] != NULL) printf("(%d,%d) ",hashArray[i]->key,hashArray[i]->data); } printf("\n");}int main() { dummyItem = (struct DataItem*) malloc(sizeof(struct DataItem)); dummyItem->data = -1; dummyItem->key = -1; insert(1, 20); insert(2, 70); insert(42, 80); insert(4, 25); insert(12, 44); insert(14, 32); insert(17, 11); insert(13, 78); insert(37, 97); printf("Insertion done: \n"); printf("Contents of Hash Table: "); display(); int ele = 37; printf("The element to be searched: %d", ele); item = search(ele); if(item != NULL) { printf("\nElement found: %d\n", item->key); } else { printf("\nElement not found\n"); } delete(item); printf("Hash Table contents after deletion: "); display();}Output
Insertion done: Contents of Hash Table: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (37,97) The element to be searched: 37Element found: 37Hash Table contents after deletion: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (-1,-1)
#include <iostream>#include <vector>using namespace std;using namespace std;#define SIZE 20struct DataItem { int data; int key;};std::vector<DataItem*> hashArray(SIZE, nullptr);DataItem* dummyItem;DataItem* item;int hashCode(int key) { return key % SIZE;}DataItem* search(int key) { //get the hash int hashIndex = hashCode(key); //move in array until an empty while (hashArray[hashIndex] != nullptr) { if (hashArray[hashIndex]->key == key) return hashArray[hashIndex]; //go to next cell //wrap around the table hashIndex = (hashIndex + 1) % SIZE; } return nullptr;}void insert(int key, int data) { DataItem* item = new DataItem; item->data = data; item->key = key; //get the hash int hashIndex = hashCode(key); //move in array until an empty or deleted cell while (hashArray[hashIndex] != nullptr && hashArray[hashIndex]->key != -1) { hashIndex = (hashIndex + 1) % SIZE; } hashArray[hashIndex] = item;}DataItem* deleteItem(DataItem* item) { int key = item->key; int hashIndex = hashCode(key); while (hashArray[hashIndex] != nullptr) { if (hashArray[hashIndex]->key == key) { DataItem* temp = hashArray[hashIndex]; hashArray[hashIndex] = dummyItem; return temp; } hashIndex = (hashIndex + 1) % SIZE; } return nullptr;}void display() { for (int i = 0; i < SIZE; i++) { if (hashArray[i] != nullptr) cout << " (" << hashArray[i]->key << "," << hashArray[i]->data << ")"; } cout << std::endl;}int main() { dummyItem = new DataItem; dummyItem->data = -1; dummyItem->key = -1; insert(1, 20); insert(2, 70); insert(42, 80); insert(4, 25); insert(12, 44); insert(14, 32); insert(17, 11); insert(13, 78); insert(37, 97); cout<<"Insertion Done"; cout<<"\nContents of Hash Table: "; display(); int ele = 37; cout<<"The element to be searched: "<<ele; item = search(ele); if (item != nullptr) { cout << "\nElement found: " << item->key; } else { cout << "\nElement not found" << item->key; } // Clean up allocated memory delete(item); cout<<"\nHash Table contents after deletion: "; display();}Output
Insertion DoneContents of Hash Table: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (37,97)The element to be searched: 37Element found: 37Hash Table contents after deletion: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (5,1666768001)
public class HashTableExample { static final int SIZE = 20; static class DataItem { int data; int key; DataItem(int data, int key) { this.data = data; this.key = key; } } static DataItem[] hashArray = new DataItem[SIZE]; static DataItem dummyItem = new DataItem(-1, -1); static DataItem item; static int hashCode(int key) { return key % SIZE; } static DataItem search(int key) { int hashIndex = hashCode(key); while (hashArray[hashIndex] != null) { if (hashArray[hashIndex].key == key) return hashArray[hashIndex]; hashIndex = (hashIndex + 1) % SIZE; } return null; } static void insert(int key, int data) { DataItem item = new DataItem(data, key); int hashIndex = hashCode(key); while (hashArray[hashIndex] != null && hashArray[hashIndex].key != -1) { hashIndex = (hashIndex + 1) % SIZE; } hashArray[hashIndex] = item; } static DataItem deleteItem(DataItem item) { int key = item.key; int hashIndex = hashCode(key); while (hashArray[hashIndex] != null) { if (hashArray[hashIndex].key == key) { DataItem temp = hashArray[hashIndex]; hashArray[hashIndex] = dummyItem; return temp; } hashIndex = (hashIndex + 1) % SIZE; } return null; } static void display() { for (int i = 0; i < SIZE; i++) { if (hashArray[i] != null) System.out.print(" (" + hashArray[i].key + "," + hashArray[i].data + ")"); } System.out.println(); }public static void main(String[] args) { insert(1, 20); insert(2, 70); insert(42, 80); insert(4, 25); insert(12, 44); insert(14, 32); insert(17, 11); insert(13, 78); insert(37, 97); System.out.print("Insertion done"); System.out.print("\nContents of Hash Table:"); display(); int ele = 37; System.out.print("The element to be searched: " + ele); item = search(37); if (item != null) { System.out.println("\nElement found: " + item.key); } else { System.out.println("\nElement not found"); } deleteItem(item); System.out.print("Hash Table contents after deletion:"); display(); }}Output
Insertion doneContents of Hash Table: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (37,97)The element to be searched: 37Element found: 37Hash Table contents after deletion: (1,20) (2,70) (42,80) (4,25) (12,44) (13,78) (14,32) (17,11) (-1,-1)
SIZE = 20class DataItem: def __init__(self, data, key): self.data = data self.key = key# Initialize the hash array with None valueshashArray = [None] * SIZE# Create a dummy item to mark deleted cells in the hash tabledummyItem = DataItem(-1, -1)# Variable to hold the item found in the search operationitem = None# Hash function to calculate the hash index for the given keydef hashCode(key): return key % SIZE# Function to search for an item in the hash table by its keydef search(key): # Calculate the hash index using the hash function hashIndex = hashCode(key) # Traverse the array until an empty cell is encountered while hashArray[hashIndex] is not None: if hashArray[hashIndex].key == key: # Item found, return the item return hashArray[hashIndex] # Move to the next cell (linear probing) hashIndex = (hashIndex + 1) % SIZE # If the loop terminates without finding the item, it means the item is not present return None# Function to insert an item into the hash tabledef insert(key, data): # Create a new DataItem object item = DataItem(data, key) # Calculate the hash index using the hash function hashIndex = hashCode(key) # Handle collisions using linear probing (move to the next cell until an empty cell is found) while hashArray[hashIndex] is not None and hashArray[hashIndex].key != -1: hashIndex = (hashIndex + 1) % SIZE # Insert the item into the hash table at the calculated index hashArray[hashIndex] = item# Function to delete an item from the hash tabledef deleteItem(item): key = item.key # Calculate the hash index using the hash function hashIndex = hashCode(key) # Traverse the array until an empty or deleted cell is encountered while hashArray[hashIndex] is not None: if hashArray[hashIndex].key == key: # Item found, mark the cell as deleted by replacing it with the dummyItem temp = hashArray[hashIndex] hashArray[hashIndex] = dummyItem return temp # Move to the next cell (linear probing) hashIndex = (hashIndex + 1) % SIZE # If the loop terminates without finding the item, it means the item is not present return None# Function to display the hash tabledef display(): for i in range(SIZE): if hashArray[i] is not None: # Print the key and data of the item at the current index print(" ({}, {})".format(hashArray[i].key, hashArray[i].data), end="") else: # Print ~~ for an empty cell print(" ~~ ", end="") print()if __name__ == "__main__": # Test the hash table implementation # Insert some items into the hash table insert(1, 20) insert(2, 70) insert(42, 80) insert(4, 25) insert(12, 44) insert(14, 32) insert(17, 11) insert(13, 78) insert(37, 97)print("Insertion done")print("Hash Table contents: "); # Display the hash table display() display() # Search for an item with a specific key (37) item = search(37) # Check if the item was found or not and print the result if item is not None: print("Element found:", item.data) else: print("Element not found") # Delete the item with key 37 from the hash table deleteItem(item) # Search again for the item with key 37 after deletion item = search(37) # Check if the item was found or not and print the result if item is not None: print("Element found:", item.data) else: print("Element not found")Output
~~ (1, 20) (2, 70) (42, 80) (4, 25) ~~ ~~ ~~ ~~ ~~ ~~ ~~ (12, 44) (13, 78) (14, 32) ~~ ~~ (17, 11) (37, 97) ~~ Element found: 97Element not found
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