Linked Lists

Linked Lists

• Dynamic Data Structure

• Applications– where amount of required memory is

determined at run-time.

Definition & Examples

• A list is a finite sequence of zero or more elements.– {a1,a2, ..., an}

• E.g. the list of prime numbers less than 20– {2,3,5,7,11,13,17,19}

• A line of text of individual characters– {h,e,l,l,o, ,w,o,r,l,d}

• A list of lists!– {{1,2, , e,g,g,s},{1, , s,a,l,a,m,i},{1,k,g,r, ,o,f, ,to,m,a,t,o,e,s}}

a1

{

a2

{

a3

{

List Operations

• Print

• Length

• Insert

• Remove

• Lookup

• Other, e.g. list cloning, sub-list.

• Error Checking

} “Running” through the list. Enumeration

Representation

a1a1 a2a2 a3a3 a4a4

a1 4

datum pointer

a2 7 a3 10 a4 0

0 1 2 4 53 6 7 8 9 10 11 12

to next element

Implementation

Node { Handle datum, Handle pointerToNextElement}

e.g. struct Node {int myDatum, struct Node *next}; or class Node {int myDatum, Node next};

1st

Head of list Tail of list

List Handle

Accessing the Data Structure

• List Handle • setData(), getData(), setNext(), getNext()

E.g. void setData(struct Node *whichNode, int value);Or Node.setData(int);

• Printing the listHandle current = head;While (notAtEndOfList(current)){

Print(current);Current = getNext(current);

}headcurrent

a1a1 a2a2 a3a3 a4a4

Access the list

voidprintTriangleList(TriListEl *list){TriListEl *x;

for (x=list;x;x=x->next)printf("->%d\n",x->datum);/* datum can be a data structure

then printTriangle (x->datum)*/}

Number of elements

inttriangleListLen(TriListEl *list){TriListEl *x;int result = 0;

for (x=list;x;x=x->next)result++;

return result;}

Insert

a1a1 a2a2 a3a3 a4a4

aNaNat position 2

a1a1 a2a2 a3a3 a4a4

aNaN

current

aN +1. create new

node

2. find handle to new position

3. update handles

4. return

Insert

// New nodeaN = new Node(theNewValue);

// Handle to positioncurrent = head;loop

until current indicates the target position

// Update handlesaN->next = current->next;current->next = aN;

a1a1 a2a2 a3a3 a4a4

aNaN

a1a1 a2a2 a3a3 a4a4

aNaN

current

aN +

TriListEl *addToTriangleList(TriListEl *list, int datum){

TriListEl *x, *result, *current, *newEl;

newEl = (TriListEl *) malloc(sizeof(TriListEl));newEl->datum = datum;newEl->next = (TriListEl *) NULL;

if (list == (TriListEl *) NULL){

result = newEl;result->next = (TriListEl *) NULL;

}else{

for (x=list;x;x=x->next){

if (x->next == (TriListEl *) NULL)break;

}current = x;current->next = newEl;current = newEl;current->next = (TriListEl *) NULL;result = list;

}return result;

}

for (x=list;x;x=x->next){

if (x->next == (TriListEl *) NULL)

break;}current = x;current->next = newEl;current = newEl;current->next = (TriListEl *) NULL;result = list;

Remove

1.find handle to removal position

2.update handles

3.free memoryfree(current);

4.return

a5a5a1a1a2a2

a3a3 a4a4current

a5a5a1a1

a2a2

a3a3 a4a4

current

Don’t forget

Lookup

a1a1 a2a2 a3a3 a4a4

current

a1a1 a2a2 a3a3 a4a4

current

a1a1 a2a2 a3a3 a4a4

current

Enumerate through list {

if (current equals target)return current;

}return NOT_FOUND;

Return Value index, handle, Boolean, numeric

list_el *getByKey(list_el *list, char *mykey){list_el *x;

for (x=list;x;x=x->next){

if (strcmp(x->key,mykey)==0)return x;

}

return (list_el *) NULL;}

List of Data Structures

• Insertion

• Removal?

Sub - Listcurrent

May be composed of simpler operations

typedef struct Triangle {Point p1,p2,p3;

} Triangle;

typedef struct List{ Triangle datum; struct List *next;

} List;

Structural Variants

• Doubly Linked List

• Cyclic List

• List of Lists

a2a2 a3a3 a4a4 a5a5a1a1 a6a6

list handle

list handle

List of lists

typedef struct TriListEl{int datum;struct TriListEl *next;

} TriListEl;

typedef struct ListList{TriListEl *datum;struct ListList *next;

} ListList;

voidprintCardinalities(ListList *list){ListList *x;int cnt = 1;

for (x=list;x;x=x->next){

printf(“%d ",triListLen(x->datum));

cnt++;}

printf("\n all elems = %d\n“,cnt);}

voidfreeListList(ListList *list){

ListList *x, *prev;

prev = (ListList *) NULL;for (x=list;x;x=x->next){

if (prev != (ListList *) NULL)free(prev);

freeTriangleList(x->datum);prev = x;

}if (prev != (ListList *) NULL)

free(prev);}

voidfreeListList(ListList *list){

ListList *x, *prev;

prev = (ListList *) NULL;for (x=list;x;x=x->next){

if (prev != (ListList *) NULL)free(prev);

freeTriangleList(x->datum);prev = x;

}if (prev != (ListList *) NULL)

free(prev);}

Abstraction

• Abstraction of Representation w.r.t. Stored Data Type

• Code Reusability

• Implementation– Pointer Abstraction C– Object abstraction Java– Templates C++

Algorithmic Variants

• Push / Pop Stack

• Enqueue, Dequeue Queues– FILO (stack)– FIFO (priority queue)

How to remember the length?

struct ListHolder {

int numberOfElements /* private, init=-1*/

ListElement *head;

}

int lengthList(struct ListHolder *)

addElement, deleteElement must update numberOfElements