Wednesday, 1 May 2013

C Program To Implement Chain Hashing (Separate Chaining With Linked List)

  • Hash table will have 'n' number of buckets.
  • To insert a node into the hash table, we need to find the hash index for the given key.  And it could be calculated using the hash function.
                 Example:  hashIndex = key % noOfBuckets

  • Move to the bucket corresponds to the above calculated hash index and insert the new node at the end of the list.
  • To delete a node from hash table, get the key from the user, calculate the hash index, move to the bucket corresponds to the calculated hash index, search the list in the current bucket to find and remove the node with the given key. Finally, remove the node with given key, if it is present.

Hash table with 5 buckets.  0, 1,2,3 and 4 are the hash indexes
+-------+
|   0    |
+-------+
|   1    |
+-------+
|    2   |
+-------+
|   3    |
+-------+
|   4    |
+-------+

Insert a node with key 33 into the hash table.
hashIndex = 33 % 5(no of buckets)
hashIndex = 3
Hash index is 3.  So, insert the new node to the bucket with hash index 3.

+-------+
|   0    |
+-------+        -----------------         ------------------
|   1    |---->| 21 | data|   -|---->| 31 | data |   -|----->X
+-------+        -----------------          -----------------
|    2   |
+-------+       ------------------
|   3    |--->| 33 | data|      |--->X
+-------+       ------------------ 
|   4    |
+-------+

Delete a node with key 31 from the hash table.
hashIndex = 31 % 5(no of buckets) = 1
Move to the bucket with above calculated hash index(1), search the list in the current bucket(bucket with index 1)to find the node with given key and delete it.

+-------+
|   0    |
+-------+        -----------------         
|   1    |---->| 21 | data|   -|---->X
+-------+        -----------------   
|    2   |
+-------+       ------------------
|   3    |--->| 33 | data|      |--->X
+-------+       ------------------ 
|   4    |
+-------+
Example Program To Implement Chain Hashing(in C):



  #include <stdio.h>
  #include <string.h>
  #include <stdlib.h>

  struct hash *hashTable = NULL;
  int eleCount = 0;

  struct node {
        int key, age;
        char name[100];
        struct node *next;
  };

  struct hash {
        struct node *head;
        int count;
  };

  struct node * createNode(int key, char *name, int age) {
        struct node *newnode;
        newnode = (struct node *)malloc(sizeof(struct node));
        newnode->key = key;
        newnode->age = age;
        strcpy(newnode->name, name);
        newnode->next = NULL;
        return newnode;
  }


  void insertToHash(int key, char *name, int age) {
        int hashIndex = key % eleCount;
        struct node *newnode =  createNode(key, name, age);
        /* head of list for the bucket with index "hashIndex" */
        if (!hashTable[hashIndex].head) {
                hashTable[hashIndex].head = newnode;
                hashTable[hashIndex].count = 1;
                return;
        }
        /* adding new node to the list */
        newnode->next = (hashTable[hashIndex].head);
        /*
         * update the head of the list and no of
         * nodes in the current bucket
         */
        hashTable[hashIndex].head = newnode;
        hashTable[hashIndex].count++;
        return;
  }


  void deleteFromHash(int key) {
        /* find the bucket using hash index */
        int hashIndex = key % eleCount, flag = 0;
        struct node *temp, *myNode;
        /* get the list head from current bucket */
        myNode = hashTable[hashIndex].head;
        if (!myNode) {
                printf("Given data is not present in hash Table!!\n");
                return;
        }
        temp = myNode;
        while (myNode != NULL) {
                /* delete the node with given key */
                if (myNode->key == key) {
                        flag = 1;
                        if (myNode == hashTable[hashIndex].head)
                                hashTable[hashIndex].head = myNode->next;
                        else
                                temp->next = myNode->next;

                        hashTable[hashIndex].count--;
                        free(myNode);
                        break;
                }
                temp = myNode;
                myNode = myNode->next;
        }
        if (flag)
                printf("Data deleted successfully from Hash Table\n");
        else
                printf("Given data is not present in hash Table!!!!\n");
        return;
  }

  void searchInHash(int key) {
        int hashIndex = key % eleCount, flag = 0;
        struct node *myNode;
        myNode = hashTable[hashIndex].head;
        if (!myNode) {
                printf("Search element unavailable in hash table\n");
                return;
        }
        while (myNode != NULL) {
                if (myNode->key == key) {
                        printf("VoterID  : %d\n", myNode->key);
                        printf("Name     : %s\n", myNode->name);
                        printf("Age      : %d\n", myNode->age);
                        flag = 1;
                        break;
                }
                myNode = myNode->next;
        }
        if (!flag)
                printf("Search element unavailable in hash table\n");
        return;
  }

  void display() {
        struct node *myNode;
        int i;
        for (i = 0; i < eleCount; i++) {
                if (hashTable[i].count == 0)
                        continue;
                myNode = hashTable[i].head;
                if (!myNode)
                        continue;
                printf("\nData at index %d in Hash Table:\n", i);
                printf("VoterID     Name          Age   \n");
                printf("--------------------------------\n");
                while (myNode != NULL) {
                        printf("%-12d", myNode->key);
                        printf("%-15s", myNode->name);
                        printf("%d\n", myNode->age);
                        myNode = myNode->next;
                }
        }
        return;
  }

  int main() {
        int n, ch, key, age;
        char name[100];
        printf("Enter the number of elements:");
        scanf("%d", &n);
        eleCount = n;
        /* create hash table with "n" no of buckets */
        hashTable = (struct hash *)calloc(n, sizeof (struct hash));
        while (1) {
                printf("\n1. Insertion\t2. Deletion\n");
                printf("3. Searching\t4. Display\n5. Exit\n");
                printf("Enter your choice:");
                scanf("%d", &ch);
                switch (ch) {
                        case 1:
                                printf("Enter the key value:");
                                scanf("%d", &key);
                                getchar();
                                printf("Name:");
                                fgets(name, 100, stdin);
                                name[strlen(name) - 1] = '\0';
                                printf("Age:");
                                scanf("%d", &age);
                                /*inserting new node to hash table */
                                insertToHash(key, name, age);
                                break;

                        case 2:
                                printf("Enter the key to perform deletion:");
                                scanf("%d", &key);
                                /* delete node with "key" from hash table */
                                deleteFromHash(key);
                                break;

                        case 3:
                                printf("Enter the key to search:");
                                scanf("%d", &key);
                                searchInHash(key);
                                break;
                        case 4:
                                display();
                                break;
                        case 5:
                                exit(0);
                        default:
                                printf("U have entered wrong option!!\n");
                                break;
                }
        }
        return 0;
  }





  Output (C Program To Perform Insertion, Deletion In Chain Hash Table):
  jp@jp-VirtualBox:$ ./a.out
  Enter the number of elements:3

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:1
  Enter the key value:3
  Name:Sally
  Age:23

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:1
  Enter the key value:33
  Name:Harry
  Age:25

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:1
  Enter the key value:7
  Name:Nick
  Age:30

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:1
  Enter the key value:35
  Name:Raj
  Age:28

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:4

  Data at index 0 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  33          Harry          25
  3           Sally          23
  
  Data at index 1 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  7           Nick           30

  Data at index 2 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  35          Raj            28

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:2
  Enter the key to perform deletion:33
  Data deleted successfully from Hash Table

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:4

  Data at index 0 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  3           Sally          23

  Data at index 1 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  7           Nick           30

  Data at index 2 in Hash Table:
  VoterID     Name          Age   
  --------------------------------
  35          Raj            28

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:3
  Enter the key to search:35
  VoterID  : 35
  Name     : Raj
  Age      : 28

  1. Insertion 2. Deletion
  3. Searching 4. Display
  5. Exit
  Enter your choice:5



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