C Program For Writing A Function To Get Nth Node In A Linked List
Write a GetNth() function that takes a linked list and an integer index and returns the data value stored in the node at that index position.
Example:
Input: 1->10->30->14, index = 2 Output: 30 The node at index 2 is 30
Algorithm:
1. Initialize count = 0 2. Loop through the link list a. If count is equal to the passed index then return current node b. Increment count c. Change current to point to next of the current.
Implementation:
C
// C program to find n'th // node in linked list #include <assert.h> #include <stdio.h> #include <stdlib.h> // Link list node struct Node { int data; struct Node* next; }; /* Given a reference (pointer to pointer) to the head of a list and an int, push a new node on the front of the list. */ void push( struct Node** head_ref, int new_data) { // Allocate node struct Node* new_node = ( struct Node*) malloc ( sizeof ( struct Node)); // Put in the data new_node->data = new_data; // Link the old list // off the new node new_node->next = (*head_ref); // Move the head to point // to the new node (*head_ref) = new_node; } // Takes head pointer of // the linked list and index // as arguments and return // data at index int GetNth( struct Node* head, int index) { struct Node* current = head; // The index of the node we're // currently looking at int count = 0; while (current != NULL) { if (count == index) return (current->data); count++; current = current->next; } /* If we get to this line, the caller was asking for a non-existent element so we assert fail */ assert (0); } // Driver Code int main() { // Start with the empty list struct Node* head = NULL; // Use push() to construct list // 1->12->1->4->1 push(&head, 1); push(&head, 4); push(&head, 1); push(&head, 12); push(&head, 1); // Check the count function printf ( "Element at index 3 is %d" , GetNth(head, 3)); getchar (); } |
Output:
Element at index 3 is 4
Time Complexity: O(n)
Space Complexity : O(1) since using constant space for nodes and variables.
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