I was wondering if anyone can give me an idea on how i can modify this function to check for duplicates, if it contains a duplicate, since duplicates are not aloowed, output a message.
Any help would greatly be appreciated.

``````template<class Type>
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
nodeType<Type> *newNode;  //pointer to create a node

bool  found;

newNode = new nodeType<Type>; //create the node
assert(newNode != NULL);

newNode->info = newItem;   //store newitem in the node
//to NULL

if(first == NULL)  //Case 1
{
first = newNode;
count++;
}
else
{
current = first;
found = false;

while(current != NULL && !found) //search the list
if(current->info >= newItem)
found = true;
else
{
trailCurrent = current;
}

if(current == first)  	//Case 2
{
first = newNode;
count++;
}
else				//Case 3
{
count++;
}
}//end else
}//end insertNode``````

<< moderator edit: added [code][/code] tags >>

It's an ordered list, so all you need to do is break off the search when the node's value is not less than the new item. To test for a duplicate, check and see if the next node has the same value as the new item:

``// …``

>do i need another while loop to check for the duplicates
Why would you need to? Since presumably the list is already in order, you stop searching for an insertion point at the same place that there would be a duplicate. The code I gave you is the complete algorithm …

Here's one example where a linked list is the appropriate structure for this: hashing, with linked lists used to handle collisions. Or any other situation where the linked list is short.

## All 9 Replies

It's an ordered list, so all you need to do is break off the search when the node's value is not less than the new item. To test for a duplicate, check and see if the next node has the same value as the new item:

``````// Empty list case
if ( first == NULL )
first = newNode;

// First node case
if ( newItem->info < first->info ) {
newNode->next = first;
first = newNode;
}

// Find an insertion point
while ( current->next != NULL && current->next->info < newItem )
current = current->next;

// Check for a duplicate
if ( current->next->info == newItem )
return DUPLICATE;
else {
newNode->next = current->next;
current->next = newItem;
}``````

since this is an ordered list and it is searching where to place the new item in the list so it is in order, do i need another while loop to check for the duplicates, i know you need to go through the whole list and compare each item by moving another pointer along, i'm just not sure where in the insertNode where to code it. it uses the linkedlist.h file which i'll sent as well. I appreciate your help, thanks one again.

``````#ifndef H_orderedLinkedListType

#include <iostream>
#include <cassert>

using namespace std;

template<class Type>
{
public:
bool search(const Type& searchItem);
//Function to determine whether searchItem is in the list.
//Postcondition: Returns true if searchItem is found in
//               the list; otherwise, it returns false

void insertNode(const Type& newItem);
//Function to insert newItem in the list.
//Postcondition: first points to the new list and newItem is
//               inserted at the proper place in the list.

void deleteNode(const Type& deleteItem);
//Function to delete deleteItem from the list.
//Postcondition: If found, the node containing deleteItem
//               is deleted from the list; first points
//               to the first node of the new list.
//               If deleteItem is not in the list, an
//               appropriate message is printed.
};

template<class Type>
{
bool found;
nodeType<Type> *current; //pointer to traverse the list

found = false;    //initialize found to false
current = first;  //start the search at the first node

while(current != NULL && !found)
if(current->info >= searchItem)
found = true;
else

if(found)
found = (current->info == searchItem); //test for equality

return found;
}//end search

template<class Type>
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
nodeType<Type> *newNode;  //pointer to create a node

bool  found;

newNode = new nodeType<Type>; //create the node
assert(newNode != NULL);

newNode->info = newItem;   //store newitem in the node
//to NULL

if(first == NULL)  //Case 1
{
first = newNode;
count++;
}
if(newItem < first->info)
{
first = newNode;
}
else
{
current = first;
found = false;

while(current != NULL && !found && current->link->info < newItem) //search the list

if(current->info >= newItem)
found = true;
else
{
trailCurrent = current;
}
cout << "No Duplicates Allowed"<<endl;
else
{
current->info = newItem;
}
if(current == first)  	//Case 2
{
first = newNode;
count++;
}
else				//Case 3
{
count++;
}
}//end else
}//end insertNode

template<class Type>
(const Type& deleteItem)
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
bool found;

if(first == NULL) //Case 1
cerr<<"Cannot delete from an empty list."<<endl;
else
{
current = first;
found = false;

while(current != NULL && !found)  //search the list
if(current->info >= deleteItem)
found = true;
else
{
trailCurrent = current;
}

if(current == NULL)   //Case 4
cout<<"The item to be deleted is not in the list."
<<endl;
else
if(current->info == deleteItem) //item to be deleted
//is in the list
{
if(first == current) 		//Case 2
{

delete current;
}
else     				//Case 3
{
delete current;
}
count--;
}
else  					//Case 4
cout<<"The item to be deleted is not in the list."
<<endl;
}
} //end deleteNode

#endif``````
``````#ifndef H_LinkedListType

#include <iostream>
#include <cassert>
using namespace std;

template <class Type>
struct nodeType
{
Type info;
};

template<class Type>
{
template<class Type>

public:
void initializeList();
//Initializes the list to an empty state.
//Postcondition: first = NULL, last = NULL,
//                count = 0
bool isEmptyList();
//Function to determine whether the list is empty.
//Postcondition: Returns true if the list is empty;
//               otherwise, returns false.

int length();
//Function to return the number of nodes in the
//list.
//Postcondition: The value of count is returned.
void destroyList();
//Function to delete all the nodes from the list.
//Postcondition: first = NULL, last = NULL,
//               count = 0
Type front();
//Function to return the first element of the list.
//Precondition: The list must exist and must not be
//empty.
//Postcondition: If the list is empty, then the
//               program terminates; otherwise,
//               the first element of the list is
//               returned.
Type back();
//Function to return the last element of the
//list.
//Precondition: The list must exist and must not
//be empty.
//Postcondition: If the list is empty, then the
//               program terminates; otherwise,
//               the last element of the list is
//               returned.

bool search(const Type& searchItem);
//Function to determine whether searchItem is in
//the list.
//Postcondition: Returns true if searchItem is found
//               in the list; otherwise, it returns
//               false.

void insertFirst(const Type& newItem);
//Function to insert newItem in the list.
//Postcondition: first points to the new list
//                and newItem is inserted at the
//                beginning of the list.

void insertLast(const Type& newItem);
//Function to return newItem at the end of the
//list.
//Postcondition: first points to the new list,
//                newItem is inserted at the end
//                of the list, and last points to
//                the last node in the list.

void deleteNode(const Type& deleteItem);
//Function to delete deleteItem from the list.
//Postcondition: If found, the node containing
//               deleteItem is deleted from the
//                list, first points to the first
//                node, and last points to the last
//                node of the updated list.

//default constructor
//Initializes the list to an empty state.
//Postcondition: first = NULL, last = NULL,
//               count = 0

//copy constructor

//destructor
//Deletes all the nodes from the list.
//Postcondition: The list object is destroyed.

protected:
int count;		//variable to store the number of
//elements in the list
nodeType<Type> *first; //pointer to the first node of
//the list
nodeType<Type> *last;  //pointer to the last node of
//the list
private:
//Function to make a copy of otherList.
//Postcondition: A copy of otherList is created
//               and assigned to this list.
};

template<class Type>
{
return(first == NULL);
}

template<class Type>
{
first = NULL;
last = NULL;
count = 0;
}

template<class Type>
{
nodeType<Type> *temp;   //pointer to deallocate the memory
//occupied by the node
while(first != NULL)    //while there are nodes in the list
{
temp = first;        //set temp to the current node
delete temp;         //deallocate memory occupied by temp
}

last = NULL;	//initialize last to NULL; first has already
//been set to NULL by the while loop
count = 0;
}

template<class Type>
{
destroyList(); //if the list has any nodes, delete them
}

template<class Type>
{
return count;
}  // end length

template<class Type>
{
assert(first != NULL);
return first->info; //return the info of the first node
}//end front

template<class Type>
{
assert(last != NULL);
return last->info; //return the info of the first node
}//end back

template<class Type>
{
nodeType<Type> *current; //pointer to traverse the list
bool found;

current = first; //set current to point to the
//first node in the list
found = false;   //set found to false

while(current != NULL && !found)		//search the list
if(current->info == searchItem)     //the item is found
found = true;
else
current = current->link; //make current point
//to the next node

return found;
}//end search

template<class Type>
{
nodeType<Type> *newNode; //pointer to create the new node

newNode = new nodeType<Type>; //create the new node

assert(newNode != NULL);	//If unable to allocate memory,
//terminate the program

newNode->info = newItem; 	   //store the new item in the node
newNode->link = first;        //insert newNode before first
first = newNode;              //make first point to the
//actual first node
count++; 			   //increment count

if(last == NULL)   //if the list was empty, newNode is also
//the last node in the list
last = newNode;
}

template<class Type>
{
nodeType<Type> *newNode; //pointer to create the new node

newNode = new nodeType<Type>; //create the new node

assert(newNode != NULL);	//If unable to allocate memory,
//terminate the program

newNode->info = newItem;      //store the new item in the node
//to NULL

if(first == NULL)	//if the list is empty, newNode is
//both the first and last node
{
first = newNode;
last = newNode;
count++;		//increment count
}
else			//the list is not empty, insert newNode after last
{
last->link = newNode; //insert newNode after last
last = newNode;   //make last point to the actual last node
count++;		//increment count
}
}//end insertLast

template<class Type>
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent; //pointer just before current
bool found;

if(first == NULL)    //Case 1; list is empty.
cerr<<"Can not delete from an empty list.\n";
else
{
if(first->info == deleteItem) //Case 2
{
current = first;
count--;
if(first == NULL)    //list has only one node
last = NULL;
delete current;
}
else  //search the list for the node with the given info
{
found = false;
trailCurrent = first;   //set trailCurrent to point to
//the first node
current = first->link;  //set current to point to the
//second node

while(current != NULL && !found)
{
if(current->info != deleteItem)
{
trailCurrent = current;
}
else
found = true;
} // end while

if(found) //Case 3; if found, delete the node
{
count--;

if(last == current)      //node to be deleted was
//the last node
last = trailCurrent;  //update the value of last

delete current;  //delete the node from the list
}
else
cout<<"Item to be deleted is not in the list."<<endl;
} //end else
} //end else
} //end deleteNode

template<class Type>
ostream& operator<<(ostream& osObject, const linkedListType<Type>& list)
{
nodeType<Type> *current; //pointer to traverse the list

current = list.first;   //set current so that it points to
//the first node
while(current != NULL) //while more data to print
{
osObject<<current->info<<" ";
}

return osObject;
}

template<class Type>
{
destroyList();
}//end destructor

template<class Type>
{
nodeType<Type> *newNode; //pointer to create a node
nodeType<Type> *current; //pointer to traverse the list

if(first != NULL)	//if the list is nonempty, make it empty
destroyList();

if(otherList.first == NULL) //otherList is empty
{
first = NULL;
last = NULL;
count = 0;
}
else
{
current = otherList.first;  //current points to the
//list to be copied
count = otherList.count;

//copy the first node
first = new nodeType<Type>;  //create the node

assert(first != NULL);

first->info = current->info; //copy the info
//the node to NULL
last = first;    		     //make last point to the
//first node
current = current->link;     //make current point to
//the next node

//copy the remaining list
while(current != NULL)
{
newNode = new nodeType<Type>;  //create a node

assert(newNode!= NULL);

newNode->info = current->info;	//copy the info
//newNode to NULL
last->link = newNode; 		//attach newNode after last
last = newNode;   			//make last point to
//the actual last node
current = current->link;	//make current point to
//the next node
}//end while
}//end else
}//end copyList

//copy constructor
template<class Type>
{
first = NULL;

copyList(otherList);

}//end copy constructor

template<class Type>
{
if(this != &otherList) //avoid self-copy
copyList(otherList);

return *this;
}

#endif``````

<< moderator edit: fixed [code][/code] tags >>

It's an ordered list, so all you need to do is break off the search when the node's value is not less than the new item. To test for a duplicate, check and see if the next node has the same value as the new item:

``````// Empty list case
if ( first == NULL )
first = newNode;

// First node case
if ( newItem->info < first->info ) {
newNode->next = first;
first = newNode;
}

// Find an insertion point
while ( current->next != NULL && current->next->info < newItem )
current = current->next;

// Check for a duplicate
if ( current->next->info == newItem )
return DUPLICATE;
else {
newNode->next = current->next;
current->next = newItem;
}``````

>do i need another while loop to check for the duplicates
Why would you need to? Since presumably the list is already in order, you stop searching for an insertion point at the same place that there would be a duplicate. The code I gave you is the complete algorithm to do this (insert into an ordered list without duplicates), all you need to do is incorporate it into your code.

If you need to ensure uniqueness then a linked list is not an appropriate data structure. Inserting into a linked list is expected to be a constant time O(1) operation. Checking for duplicates during the insert is going to change that.

You might want to consider a LinkedHashMap. It is basically a LinkedList in which all the Nodes are also kept in a hash. The expected insert time is still constant and duplicate entries can be checked for upon insertion in the hash.

I initially thought you were asking how to check for duplicate node pointers in a linked list , but it appears that you really want to avoid inserting duplicate objects. Please correct me if I am wrong.

Here's one example where a linked list is the appropriate structure for this: hashing, with linked lists used to handle collisions. Or any other situation where the linked list is short.

>If you need to ensure uniqueness then a linked list is not an appropriate data structure.
How do you know? The OP never mentioned how this list is going to be used, so it could very well be an appropriate data structure.

>Inserting into a linked list is expected to be a constant time O(1) operation.
Only if you make certain assumptions, like that the insertion will only be at the head of the list, or at the tail and then only if there is a tail pointer. The average expected time complexity for inserting into a linked list in the general case is O(N/2).

>You might want to consider a LinkedHashMap.
This is not Java. In C++, he would have to implement the functionality of a LinkedHashMap.

>Inserting into a linked list is expected to be a constant time O(1) operation.
Only if you make certain assumptions, like that the insertion will only be at the head of the list, or at the tail and then only if there is a tail pointer. The average expected time complexity for inserting into a linked list in the general case is O(N/2).

And the worst case time complexity is O(N/100000000).

:cool:

And the worst case time complexity is O(N/100000000).

:cool:

There are times when I can't tell if you're joking or not. :confused:

I had to do this and found a much simpler fix, in the insert method starting with the first while(which I included to help) use this:

``````         while (current != NULL && !found) //search the list
if (current->info == newItem)
{
cout << "Error" <<endl;
}
else //If there are no duplicates then proceed with the input of the list
{ //Inserted bracket
if (current->info >= newItem)
found = true;
else
{
trailCurrent = current;