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[\<- Notes 01/29](01-29.md)
---
# Linked Lists Continued
Recall: Linked List Declaration:
```
#define NODE struct node
struct node{
char name[20];
int number;
NODE *next;
};
NODE *head = NULL;
```
## Deleting a Node
- if the Linked List only has one Node:
```
head->next = NULL;
free(p); //where p is a pointer to the deleted node
```
- if the Linked List has more than one Node and you want to delete the first Node:
| Visual Representation | | | | | | | | | |
| - | - | - | - | - | - | - | - | - | - |
| **Before:** | head | -> | n1 | -> | n2 | -> | n3 | | |
| **After:** | head | -> | n2 | -> | n3 | | | | |
```
head = head->next;
free(p); //where p is a pointer to the deleted node
```
the order of steps is important (freeing memory should always be the last step)
- Find nodes with matching numbers 'n' (p and q are pointers pointing to the nodes they are in):
| Visual Representation | | | | | | | | | |
| - | - | - | - | - | - | - | - | - | - |
| **Before:** | head | -> | n1 (p) (q)| -> | n2 | -> | n3 | | |
```
NODE *p, *q;
p = q = head;
while(p->number != n && p != NULL){
q = p;
p = p->next; //traverse in n1 until it finds 'n' or it gets to the end (NULL);
}
```
| Visual Representation | | | | | | | | | |
| - | - | - | - | - | - | - | - | - | - |
| **After above While loop:** | head | -> | n1 | -> | n2 (q)| -> | n3 (p)| | |
```
//eventually...
q->next = NULL;
free(p);
```
Conditional Statements to determine info about the above Linked List (where we want to delete the Node 'p' is pointing to):
```
if(head->next == NULL){ //there is only one node (head)
head = head->next;
free(p);
}
else{
if(p == head){ //this is the First Node
head = head->next;
free(p);
}
else if(p->next == NULL){ //this is the last node
q->next = NULL;
free(p);
}
else{ //the node is somewhere in the middle of the list
q->next = p->next;
free(p);
}
}
```
- It can be helpful to define a tail pointer in addition to the head pointer
- the tail pointer would point to the end of the list
|
