Insert at end

Challenge

Append a new node to the end of a singly linked list and return the head.

The grader supplies the same node type as the previous exercise:

typedef struct node { int data; struct node *next; } node_t;

Task

Implement node_t *insert(node_t *head, int value) that allocates a new node holding value, appends it at the end of the list, and returns the (possibly new) head. No main — the grader calls it.

Input

• head: pointer to the first node, or NULL for an empty list.
• value: the int to store in the new tail node.

Output

The head of the list after appending. If head was NULL, the new node becomes the head and is returned.

Example

insert(NULL, 1)              ->   list 1
insert(1->2, 3)             ->   list 1->2->3

Edge cases

• Inserting into an empty list (head == NULL) returns the new node as the head.

Rules

• Allocate the new node with malloc.

Input format

head (or NULL) and the int value for the new tail node.

Output format

The head of the list after appending the new node.

Constraints

Allocate the new node with malloc; an empty list returns the new node.

Starter code

#include <stdlib.h>

node_t *insert(node_t *head, int value) {
    /* TODO */
    return head;
}

Common mistakes

Failing to update *head when the initial list is empty; traversing with curr instead of curr->next and dropping the pointer.

Edge cases to handle

Inserting into an empty list (*head == NULL); list with a single node; memory allocation failure for the new node.