Wednesday, March 11, 2009

Linked list sorted in an ascending order

Again to practice some of skills I wrote linked list sorted in an ascending order. It is very simple example and it performs only two operation:
  • inserting an item into the appropriate position in the list
  • printing the whole list on the screen
The following code is placed in the public domain. Use it as you wish. The code can be downloaded with the solution project file for MS Visual Studio 2008 from here.

// LinkedList.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include

/*
The supplied C code fragment is intended to implement a linked list of
integers stored in ascending order. Each element of the list is a struct
of type Item holding the integer value, a pointer pred to the previous
element, if any, and a pointer succ to the succeeding element, if any. The
variable head points to the ?rst element in the list, and tail points to
the last element. Initially, both head and tail are NULL. The function
insert is intended to insert its argument x into the list. If x is already in
the list, insert should do nothing.
*/

using namespace std;

struct Item {
int value; // the integer value
Item* succ; // succeeding value
Item* pred; // preceding value
};

Item* head = NULL;
Item* tail = NULL;

Item* createItem(int x, Item* succ, Item* pred)
{
Item* item = new Item;
item->value = x;
item->succ = succ;
item->pred = pred;

return item;
}

/**
Insert x into linked list

There are 5 possible cases, any four of these will suffice
- list is initially empty
- x is smaller than any number in the list
- x is larger than any number in the list
- x is already in the list
- the normal case i.e. none of the above

*/

void insert(int x)
{
Item *p = head , *q;
if(!p) {
// add the first item
head = tail = createItem(x,NULL,NULL);
}
else if (x > tail->value){
// add the largest item in the list
tail->succ = createItem(x,NULL,tail);
tail = tail->succ;
}
else{
while (x > p->value)
p = p->succ;

if (x==p->value)
// do not add itme because it already exists
return;

// add the item before p because x < q =" createItem(x,">pred); // create item, pass the succesor and the predcesor
q->succ->pred = q; // modify the succesor of q so that it points to q
q->pred->succ = q; // modify the predcesor of q so that it points to q
}
}

void printList(void)
{
Item* p = head;
int counter = 0;

cout << "------------------------------------------------------------" <<>value << p =" p-">succ;
}
}

int _tmain(int argc, _TCHAR* argv[])
{
cout << "Ascending linked list demonstration." << i =" 0;">


The output of the program is as follows:

Ascending linked list demonstration.
--------------------------------------
Item number:0 Item value:1
--------------------------------------
Item number:0 Item value:1
Item number:1 Item value:10
--------------------------------------
Item number:0 Item value:1
Item number:1 Item value:5
Item number:2 Item value:10
--------------------------------------
Item number:0 Item value:1
Item number:1 Item value:5
Item number:2 Item value:10


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