linked list c and data structures baojian hua bjhua@ustc.edu.cn

Linked List

C and Data StructuresBaojian Hua

bjhua@ustc.edu.cn

Recap The extensible array-based

implementation of linear list: may be too slow

insert or delete operations involve data movement

may be too space waste only a small portion of the allocated space is

occupied with data

General computer science idea “pay as you go”

Polymorphic Abstract Data Types in C// recall the poly ADT:

#ifndef LIST_H

#define LIST_H

typedef void *poly;

typedef struct listStruct *list;

list newList ();

int length (list l);

poly nth (list l, int n);

void insert (list l, poly x, int i);

poly delete (list l, int i);

void foreach (list l, void (*f)(poly));

#endif

Implementation Using Linked List

Linked list is a self-reference structure:

to simplify operations, we add a unique head node “head”

“head” does not belong to the list may hold meta information of the list

head…

Linked List-based Implementation// Turn the above figure into C, we have:// in file “linkedList.c”#include <stdlib.h>#include “list.h”struct listStruct{ poly data; list next;};

data

next

data

next

data

next

head …

Operation: “newList”// “new” returns an empty list, which consists of// a single head node.list newList (){ list l = (list)malloc (sizeof (*l)); l->data = NULL; // Why this? l->next = NULL; return l;}

/\

/\

l

Operation: “length”int length (list l){ list p = l->next; int n = 0; while (p) { p = p->next; n++; } return n;}

data

next

data

next

data

next

l …p

n==0

Operation: “length”int length (list l){ list p = l->next; int n = 0; while (p) { p = p->next; n++; } return n;}

data

next

data

next

data

next

l …p

n==1

Operation: “length”int length (list l){ list p = l->next; int n = 0; while (p) { p = p->next; n++; } return n;}

data

next

data

next

data

next

l …p

n==2

Operation: “length”int length (list l){ list p = l->next; int n = 0; while (p) { p = p->next; n++; } return n;}

data

next

data

next

data

next

l …p

n==3

Operation: “nth”poly nth (list l, int n){ list p = l->next; int i = 0; if (n<0 || n>=length(l)) error (“invalid index”);

while (i!=n) { p = p->next; i++; } return p;}

Operation: “nth”

data

next

data

next

data

next

l …

n==2

p

i==0

data

next

data

next

data

next

l …

n==2

p

i==1

data

next

data

next

data

next

l …

n==2

p

i==2

Operation: “insert”void insert (list l, poly x, int n){ // 1. change the “next” field of pointer t; // 2. change the “next” field of element (n-1) …;}

data

next

data

next

data

next

l …

n==2

x

nextt

we’d search pointer p

Operation: “insert”void insert (list l, poly x, int n){ list p; if (n<0 || n>length(l)) error (“invalid index”);

// search pointer p points to position n-1 p = n? (nth (l, n-1)) : l;

Operation: “insert” // continued…

// Step #1: cook list node:list temp = (list)malloc (sizeof (*temp));

temp->data = x; // Step #2: temp points to n-th data item temp->next = p->next; // Step #3: link temp onto list p->next = temp; return;}

Operation: “delete”poly delete (list l, int n){ // The key step is to search pointer p // Leave this as exercise.

// See Lab #3. …;}

data

next

data

next

data

next

l …

n==2we’d search pointer p

Operation: “foreach”void foreach (list l, void (*f)(poly)){ list p = l->next; while (p) { f (p->data); p = p->next; }}

data

next

data

next

data

next

l …

Linked List Summary Linked list:

better space usage---no waste good time complexity

insert or delete take linear time but have to search the data sequential, :-(

Can be further generalized: circular linked list doubly linked list doubly circular linked list

Circular Linked List All the pointers forms a circle

Note that the first node has two fields head: points to the head of the list tail: points to the tail of the list

head

tail

data

next

data

next

data

next

l

Circular Linked List---Implementation// in file “clist.c”

struct listStruct

{

struct node *head;

struct node *tail;

};

struct node

{

poly data;

struct node *next;

}

head

tail

data

next

data

next

data

next

l

Linear List Application #1: Polynomials Polynomials:

where ciR and n Nat uniquely determined by a linear list:

For this representation, all the list operations apply

Linear List Application: Polynomials Space waste:

Consider this:

20001 items with 3 non-zeros A refined representation:

ci<>0 for 0<=i<=m Ex:

Polynomial ADT: Interface Abstract data type: polyn

represent the polynomial data type operations:polyn newPolyn (); // an empty polynpolyn add (polyn p1, polyn p2);real value (polyn p, real x0); // p(x0)polyn mult (polyn p1, polyn p2);// add an item c*x^n, which does not appear in pvoid insert (polyn p, real c, int n);

Polynomial ADT in C: Interface// in file “polyn.h”#ifndef POLYN_H#define POLYN_H

typedef struct polynStruct *polyn;

polyn newPolyn (); polyn add (polyn p1, polyn p2);real value (polyn p, real x0); polyn mult (polyn p1, polyn p2);void insert (polyn p, real c, int n);

#endif

Polynomial ADT in C: Implementation// in file “polyn.c”#include “linkedList.h”#include “polyn.h”

struct polynStruct{ linkedList coefExps;};// where “coefExps” is a list of tuples: (c, n)// one way to read “list coefExps” is:// list<tuple<double, nat>> coefExps// However, C does not support this style of// declaration… :-(

Operation: “newPolyn”polyn newPolyn ()

{

polyn p = (polyn)malloc (sizeof (*p));

// use a linked list internally

p->coefExps = newLinkedList ();

return p;

}

Operation: “insert”void insert (polyn p, real c, nat n)

{

// could we use “double” and “int”, instead of

// “real” and “nat”?

tuple t = newTuple (c, n);

linkedListInsertAtTail (p->coefExps, t);

return;

}

// Leave other functions as exercises.

Change to the Head#include <stdlib.h>

#include “linkedList.h”

#include “tuple.h”

#include “polyn.h”

struct polyn

{

linkedList coefExps;

};

Linear List Application#2: Dictionary

Dictionay:

where ki are keys and vi are value all ki are comparable and distinct How can dict’ be represented in compu

ters? many ideas (we’d discuss some in future) for now, we make use of a linear list

Dictionary ADT: Interface

Abstract data type: dict represent the dictionary data type

operations:dict newDict (); // an empty dict

void insert (dict d, poly key, poly value);

poly lookup (dict d, poly key);

poly delete (dict d, poly key);

“dict” ADT in C: Interface// in file “dict.h”#ifndef DICT_H#define DICT_H

typedef struct dictStruct *dict;

dict newDict (); void insert (dict d, poly key, poly value);poly lookup (dict d, poly key);poly delete (dict d, poly key);

#endif

“dict” ADT in C: Implementation// in file “dict.c”

#include “linkedList.h”

#include “dict.h”

struct dictStruct

{

linkedList l;

};

Operations: “new”dict newDict ()

{

dict d = (dict)malloc (sizeof (*d));

d->l = newLinkedList ();

return d;

}

Operations: “insert”void insert (dict d, poly key, poly value)

{

tuple t = newTuple (key, value);

linkedListInsertAtHead (d->l, t);

return;

}

// Leave other functions as programming

// exercises.