Head null delete head head n else if head next key

head = NULL;
delete head;
head = n;
} else if (head->next->key == oldKey) {
Node* n = head->next;
head->next = head->next->next;
delete n;
} else {
remove(head->next, oldKey);
}
}
}
/**
* Insert a new Node (with key=newKey) after an existing Node (with key=oldKey)
* If there is no existing Node with key=oldKey, then no action.
* PRE: head is the first Node in a linked_list (if NULL, linked_list is empty)
* PRE: oldKey is the value to look for (in the key of an existing Node)
* PRE: newKey is the value of the key in the new Node (that might be inserted)
* POST: if no Node with key=oldKey was found, then the linked_list has not
changed
* POST: else a new Node (with key=newKey) is right after the Node with key =
oldKey.
*/
void insert_after(Node* head, int oldKey, int newKey){
if (head != NULL) {
if (head->key == oldKey) {
Node* n = new Node;
n->key = newKey;
n->next = head->next;
head->next = n;
} else {
insert_after(head->next, oldKey, newKey);
}
}
}
/**
* Create a new linked_list by merging two existing linked_lists.
* PRE: list1 is the first Node in a linked_list (if NULL, then it is empty)
* PRE: list2 is the first Node in another linked_list (if NULL, then it is
empty)
* POST: A new linked_list is returned that contains new Nodes with the keys

from
* the Nodes in list1 and list2, starting with the key of the first Node of
list1,
* then the key of the first Node of list2, etc.
* When one list is exhausted, the remaining keys come from the other list.
* For example: [1, 2] and [3, 4, 5] would return [1, 3, 2, 4, 5]
*/
Node* interleave(Node* list1, Node* list2){
Node* head = NULL;
Node* curr = head;
while(list1 && list2) {
Node* n1 = new Node;
Node* n2 = new Node;
n1->key = list1->key;
n2->key = list2->key;
n1->next = n2;
n2->next = NULL;
if(!head) {
head = n1;
} else {
curr->next = n1;
}
curr = n2;
list1 = list1->next;
list2 = list2->next;
}
while(list2) {
Node* n2 = new Node;
n2->key = list2->key;
n2->next = NULL;
if(!head) {
head = n2;
curr = head;
} else {
curr->next = n2;
curr = curr->next;
}
list2 = list2->next;
}
while(list1) {
Node* n1 = new Node;
n1->key = list1->key;
n1->next = NULL;
if(!head) {
head = n1;
curr = head;
} else {
curr->next = n1;
curr = curr->next;
}
list1 = list1->next;
}
return head;
}