Question

c programming

A linked list is a linear data structure that allows us to add and remove items from the list very quickly, by simply changing a few pointers. There are many different variations of linked lists. We have studied the doubly-linked, circular, with a dummy-header-node version of a linked list. In the class notes we studied several functions to manipulate a Linked List. For this assignment you must write the code for the following additional linked list functions: addFirst, removeLast, clear, and set. The provided source code contains a stub for each of these functions, together with a description of what the function should do. You must complete the body of each of these functions. You must write each of these functions from scratch. You must not invoke the existing list functions. The addFirst function will insert a new data item into the list at position 0 (in front of all the items already in the list). The removeLast function deletes the last item in the list (at position size-1), and returns the data that was deleted from the List. If removeLast is invoked on an empty List, then it should output an error message, leave the list unchanged, and return the NULL pointer. The effect of the clear function is to make the List become an empty List. The set function should alter the value of the data at the specified location in the list. The size of the list remains the same. The set function should return the item that was deleted from the List (because it was overwritten by the new item). If the set function references an illegal index, then it should print an error message, and the list should be unchanged. You should implement each of these functions in the most efficient manner possible. Your function should not take O(n) time when an O(1) solution is possible. Also, the set function should be as efficient as possible. If the target location (e.g., index) is more than halfway down the linked list, then the traversal should start from the rear of the list and move leftwards.

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

typedef struct {

char *name;
char *major;

} Student;

typedef struct node { // represents one node in a Linked List

void *data; // pointer to data associated with this node
struct node *next; // pointer to next node in List
struct node *prev; // pointer to previous node in List

} Node;

typedef struct {

Node *header; // pointer to the "dummy header node" of
// the Linked List
int size; // number of nodes in the Linked List

} LinkedList;

// function proto-types
void createList ( LinkedList *someList );
void addEnd( LinkedList *someList, void *newElement );
void *delete( LinkedList *someList, int position );
int indexOf( LinkedList *someList, char *target );
void outputList( LinkedList *someList );

int main() {

LinkedList myList;

LinkedList *roster = NULL;
outputList ( roster );

roster = &myList;
createList ( roster ); // initialize the fields of the list
outputList ( roster );

Student a, b, c, d, e, f, g;

a.name = "alice"; a.major = "ART";
b.name = "bob"; b.major = "BIO";
c.name = "chad"; c.major = "CHM";
d.name = "dan"; d.major = "DNC";
e.name = "ed"; e.major = "ENG";
f.name = "fran"; f.major = "FRN";
g.name = "gian"; g.major = "GEO";

addEnd ( roster, &a );
addEnd ( roster, &b );
addEnd ( roster, &c );
addEnd ( roster, &d );

outputList ( roster );

Student *someStudent;
someStudent = delete ( roster, 1 );
printf ( "\nAfter removing position 1 the list is:\n" );
outputList ( roster );
someStudent = delete ( roster, 0 );
printf ( "\nAfter removing position 0 the list is:\n" );
outputList ( roster );
someStudent = delete ( roster, 1 );
printf ( "\nAfter removing position 1 the list is:\n" );
outputList ( roster );
someStudent = delete ( roster, 0 );
printf ( "\nAfter removing position 0 the list is:\n" );
outputList ( roster );

addEnd ( roster, &a );
addEnd ( roster, &b );
addEnd ( roster, &c );
addEnd ( roster, &d );
outputList ( roster );

int pos;
pos = indexOf ( roster, "alice" );
printf ( "\nThe position of \"alice\" is: %d\n", pos );
pos = indexOf ( roster, "bob" );
printf ( "The position of \"bob\" is: %d\n", pos );
pos = indexOf ( roster, "chad" );
printf ( "The position of \"chad\" is: %d\n", pos );
pos = indexOf ( roster, "dan" );
printf ( "The position of \"dan\" is: %d\n\n", pos );
}

// Initially the List is empty
// We must create memory for the "dummy header node"
void createList ( LinkedList *someList )
{
someList->size = 0;

someList->header = malloc ( sizeof (Node) );

someList->header->data = NULL;
someList->header->next = someList->header;
someList->header->prev = someList->header;
}

// add the new data element to the end of the List
void addEnd( LinkedList *someList, void *newData )
{
Node *lastNode = someList->header->prev;

Node *newNode = malloc ( sizeof ( Node ) );

newNode->data = newData; // set the fields of the new Node
newNode->next = someList->header;
newNode->prev = someList->header->prev;

someList->header->prev->next = newNode; // splice-in the newNode
someList->header->prev = newNode; // into the List

someList->size++;
}

// remove the item in the given positionn in the List, and
// return the data
void *delete ( LinkedList *someList, int position )
{
if ( position < 0 || position >= someList->size ) {
printf("ERROR - illegal position in the list, aborting program\n");
exit(1);
}

// walk down the list until we reach the node to be removed

Node *temp = someList->header;
for ( int i=0; i <= position; i++ )
temp = temp->next;

void *removedData = temp->data;

temp->prev->next = temp->next; // splice-out the Node
temp->next->prev = temp->prev;

someList->size--;

free( temp ); // free-up the memory of the deleted Node

return ( removedData );
}

// locate the position in the list of the Student whose name
// equals the given target.
// return -1 if not found
int indexOf( LinkedList *someList, char *target )
{
// walk down the list until we reach the Node with the given
// target name. Stop the loop if we wrap-around the list

Node *temp = someList->header->next;

int currPos = 0; // current position in the list

while ( temp != someList->header ) {

// casting is needed since temp--> data is (void *)
char *currFirstName = ( (Student *) temp->data )->name;

if ( strcmp ( currFirstName, target ) == 0 )
return currPos; // target has been found

temp = temp->next;

currPos++;
}

return ( -1 ); // target was not found in the List
}

// output the contents of the List
void outputList( LinkedList *someList )
{
if ( someList == NULL )
printf ( "The List has not been created yet\n\n" );

else if ( someList->size == 0 )
printf ( "The List is empty\n\n" );

else {
printf ( "The List is: " );

Node *temp = someList->header->next;

for ( int num = 0; num < someList->size; num++ ) {

printf("[%s, ",
( (Student *) temp->data )->name );
printf("%s], ",
( (Student *) temp->data )->major );

temp = temp->next;
}
printf ("\n\n" );
}
}

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