C in 100 Seconds: Linked List Insert and Delete

Linked List — Insert and Delete

Three core operations on a linked list: insert at the head, insert at the tail, and delete by value. Each one is about rewiring pointers.

Insert at Head

Node *insert_head(Node *head, int value) {
  Node *n = create_node(value);
  n->next = head;
  return n;
}

Create a new node, point its next to the current head, and return the new node. The caller updates head: head = insert_head(head, 5);

Insert at Tail

void insert_tail(Node *head, int value) {
  Node *n = create_node(value);
  Node *c = head;
  while (c->next != NULL) {
    c = c->next;
  }
  c->next = n;
}

Walk to the last node (where next is NULL), then link the new node there.

Delete by Value

Node *delete_node(Node *head, int value) {
  if (head->data == value) {
    Node *next = head->next;
    free(head);
    return next;
  }
  Node *c = head;
  while (c->next != NULL && c->next->data != value) {
    c = c->next;
  }
  if (c->next != NULL) {
    Node *temp = c->next;
    c->next = temp->next;
    free(temp);
  }
  return head;
}

Two cases: if the target is the head, free it and return the next node. Otherwise, find the node before the target, rewire around it, and free.

Student Code

Try it yourself: episode43/listops.c