Code for Reversing Linked List with Recursion, using STL
#include<iostream>
#include<conio.h>
#include<list>
using namespace std;
template<typename T>
class node
{
public:
T data;
node<T> *next;
node(){ next = NULL; }
node(const T& item, node<T> *nextnode = NULL)
{
data = item;
next = nextnode;
}
};
template<typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse(node<T> *front);
public:
Reverse_list(){ head = NULL; }
//template<typename T>
void Reverse();
template<typename T>
void Display( list<T>& alist );
};
int main()
{
Reverse_list <int> rl;
list<int> intlist;
int size, no;
cout << "Size of List ?? ";
cin >> size;
for (int i = 1; i <= size; i++)
{
cout << "Enter the " << i <<" "<< "element";
cin >> no;
intlist.push_front(no);
}
rl.Display(intlist);
rl.Reverse();
rl.Display(intlist);
_getch();
return 0;
}
template<typename T>
void Reverse_list<T>::Display(list<T>& alist)
{
list<int>::iterator iter = alist.begin();
while (iter != alist.end())
{
cout << *iter << " ";
iter++;
}
}
template<typename T>
void Reverse_list<T>::reverse(node<T> *front)
{
if (front->next == NULL)
{
head = front;
return;
}
reverse(front->next);
node<int> *back = front->next;
back->next = front;
front->next = NULL;
}
template<typename T>
void Reverse_list<T>::Reverse()
{
reverse(head);
}
The above code generates 2 errors.
Error 1) No instance of function template matches the argument list. ( No error number.)
If I remove line 1 ( mentioned in a code ) then above error is no more. ( Why? )
Error 2) C2783: 'void Reverse_list::Reverse1(void)' : could not deduce template argument for 'T'
How to solve above errors.
In above program , I wanted to pass " head" node ( which is private ) as
argument to Reverse function. But we can not access private member outside of the class. So I passed indirectly. Is this a correct way of passing ?? Or there is some other way of accessing private data ??
I'm not sure to understand your intentions but...
You're trying to declare a method (reverse()) inside another method (Reverse()) ? Uhmmm....
We return to this later.
Imagine that the following instruction is correct instruction of Reverse_list<T>::Reverse()
node<T> *back = front->next;
Why you declare back as a pointer to a generic Node<T> when you assign front->next (so a specific Node<int>) to it?
If you define back as a node<int> pointer, the method Reverse() has no longer reason to be a template (dependant from T) method. And you can avoid both errors.
With your actual code, when you call
rl.Reverse();
you call a template method but the compiler doesn't know how to determine the type T. You could explicit it in this way
rl.Reverse<int>();
but, as written before, I thik it's better if you remove the whole template part.
Or, alternatively, you can transform the whole class in a template class; where head is a pointer to a generic Node<T>, not a specifica Node<int>.
Something like (if I understand correctly your intentions)
template <typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse (node<T> * front);
public:
Reverse_list() : head(NULL)
{ }
void Reverse();
void Display(list<T>& alist);
};
template<typename T>
void Reverse_list<T>::reverse (node<T> * front)
{
if (front->next == NULL)
{
head = front;
return;
}
reverse(front->next);
node<T> *back = front->next;
back->next = front;
front->next = NULL;
}
template<typename T>
void Reverse_list<T>::Reverse()
{ reverse(head); }
In this case, in main(), rl should be declared as
Reverse_list<int> rl;
fixing T as int, and the call to Reverse() should be
rl.Reverse();
--- EDIT 2016.05.10 ---
With the "template Reverse_list" solution, you should correct three points (at last).
1) in Reverse_list class declaration, you have commented the template<typename T> row before void Reverse(); good; you should delete (comment) the same line (for the same reason) before void Display( list<T>& alist );; so the class become
template<typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse(node<T> *front);
public:
Reverse_list(){ head = NULL; }
//template<typename T>
void Reverse();
//template<typename T>
void Display( list<T>& alist );
};
2) Display() now is a method of a templated class; so the line
list<int>::iterator iter = alist.begin();
become
list<T>::iterator iter = alist.begin();
3) reverse() now is a method of a templated class; so the line
node<int> *back = front->next;
become
node<T> *back = front->next;
I realize the title isn't too descriptive so here are the details. I'm implementing my own Binary Tree class in C++. I have written a template Node class and template Binary Tree class already, for the most part, and am stuck on something. I created an empty binary tree (root node is null) and when I try to set that node it fails miserably. here is the code and more explanation:
template<class T> class Node
{
T _key;
Node<T> *_leftChild;
Node<T> *_rightChild;
public:
Node();
Node(T key);
Node(T key, Node<T> *leftChild, Node<T> *rightChild);
~Node();
bool hasLeftChild();
bool hasRightChild();
void setKey(T key);
void setLeftChild(Node<T> *node);
void setRightChild(Node<T> *node);
T getKey();
Node<T>* getLeftChild();
Node<T>* getRightChild();
bool compare(Node<T> *compareNode); // return true if this.Node < compareNode
};
Node implementation not really necessary.. ( I dont think ) it's quite long.
#include "Node.cpp"
#include <iostream>
using namespace std;
template<class T> class BinaryTree
{
Node<T> *_root;
public:
BinaryTree();
BinaryTree(Node<T> *root);
~BinaryTree();
Node<T>* getRoot();
void insert(Node<T> **root, Node<T> *node);
};
template<class T>
BinaryTree<T>::BinaryTree()
{
this->_root = NULL;
}
template<class T>
BinaryTree<T>::BinaryTree(Node<T> *root)
{
this->_root = root;
}
template<class T>
BinaryTree<T>::~BinaryTree()
{
// delete stuff
}
template<class T>
Node<T>* BinaryTree<T>::getRoot()
{
return this->_root;
}
template<class T>
void BinaryTree<T>::insert(Node<T> **root, Node<T> *node)
{
if(!*root)
{
*root = node;
}
}
Main:
BinaryTree<int> *tree = new BinaryTree<int>();
Node<int> *root = tree->getRoot();
Node<int> **root1 = &root;
cout << tree->getRoot() << endl;
Node<int> *noChildrenNode = new Node<int>(2);
tree->insert(&root1, noChildrenNode);
cout << tree->getRoot() << endl;
Inserts current functionality is just supposed to replace the NULL root pointer to the node pointer passed in as a parameter. The failing miserably part is since the pointer is a copy it isn't actually setting the root node.. but I can't seem to figure out how to set up a pointer to a pointer to the root node so it can be altered.. I've got to be close and any help will be MUCH appreciated.
Thanks
First, you've got to include the exact text of any error messages. "fails miserably" is not adequate.
I think you want
root = node;
Not
*root = node;
Because if root is null, using *root is a null pointer exception.
I am creating a class LinkedList. I am having difficulty adding another node to my list.
Here is what I have so far:
template<typename T>
class LinkedList
{
private:
T element;
T *next;
public:
LinkedList();
LinkedList(T element);
void add(LinkedList<T> &otherList);
void print();
};
template<typename T>
LinkedList<T>::LinkedList()
{
next = NULL;
}
template<typename T>
LinkedList<T>::LinkedList(T element)
{
this->element = element;
next = NULL;
}
template<typename T>
void LinkedList<T>::add(LinkedList<T> &otherList)
{
next = &otherList;
}
template<typename T>
void LinkedList<T>::print()
{
LinkedList<T> *current = this;
while (current != NULL)
{
std::cout << current->element;
current = current->next;
}
}
int main()
{
LinkedList<std::string> myFirst("First");
LinkedList<std::string> mySecond("Second");
myFirst.add(mySecond);
myFirst.print();
return 0;
}
This works however if I make the change:
void add(const LinkedList<T> &otherList);
template<typename T>
void LinkedList<T>::add(const LinkedList<T> &otherList)
{
next = &otherList; //now an error right here
}
Then I get an error stating:
Assigning to 'LinkedList<std::__1::basic_string<char> > *' from incompatible type 'const LinkedList<std::__1::basic_string<char> > *'
Why is it I get this error?
next is a T*, and you're trying to assign a const LinkedList<T>* to it.
I suppose you meant something like next = &(otherList.element) (though even then I think your list semantics are somewhat broken — elements shouldn't typically be shared by multiple containers unless you're very, very clear about the ownership semantics).
Contrary to your claims, your first program doesn't work either for the same reason.
I am a bit new to using multi-files. I have this very simple code for a linked list, but when I debug, it "stops working".
This problem has occured with me several times before. I want to know is there something wrong with my "linked list" code? Or is something wrong with the multi-files organization?
Any help would be highly appreciated.
======================================
//linkedListMAIN.cpp
#include "linkedlist.cpp"
void main()
{
linkList<int> l;
l.append(5);
l.traverse();
}
======================================
//linkedList.h
#include<iostream>
using namespace std;
template <class T>
class linkList
{
private:
struct node
{
T data;
node *next;
};
node *head;
node *tail;
int noOfEl;
public:
linkList()
{
noOfEl = 0;
head=tail=NULL;
}
void traverse();
int length();
void insertAt(T, int);
T delAt(int);
void append(T);
void clear();
};
======================================
//linkedList.cpp
#include "linkedlist.h"
template <class T>
void linkList<T>:: traverse()
{
node<T> *current=head;
if(head == NULL)
{
cout<<"List empty."<<endl;
}
while(current != NULL)
{
cout<<current->data;
current = current->next;
}
}
template <class T>
void linkList<T>::append(T data)
{
node< *newNode= new node;
newNode->next = NULL;
tail->next = newNode;
tail = newNode;
noOfEl++;
}
You should not include the .cpp in inkedListMAIN.cpp but the header (.h). Also unless you are using c++11 you will have to put the class definition of templated classes in the header.
EDIT -- Answered below, missed the angled braces. Thanks all.
I have been attempting to write a rudimentary singly linked list, which I can use in other programs. I wish it to be able to work with built-in and user defined types, meaning it must be templated.
Due to this my node must also be templated, as I do not know the information it is going to store. I have written a node class as follows -
template <class T> class Node
{
T data; //the object information
Node* next; //pointer to the next node element
public:
//Methods omitted for brevity
};
My linked list class is implemented in a seperate class, and needs to instantiate a node when adding new nodes to the end of the list. I have implemented this as follows -
#include <iostream>
#include "Node.h"
using namespace std;
template <class T> class CustomLinkedList
{
Node<T> *head, *tail;
public:
CustomLinkedList()
{
head = NULL;
tail = NULL;
}
~CustomLinkedList()
{
}
//Method adds info to the end of the list
void add(T info)
{
if(head == NULL) //if our list is currently empty
{
head = new Node<T>; //Create new node of type T
head->setData(info);
tail = head;
}
else //if not empty add to the end and move the tail
{
Node* temp = new Node<T>;
temp->setData(info);
temp->setNextNull();
tail->setNext(temp);
tail = tail->getNext();
}
}
//print method omitted
};
I have set up a driver/test class as follows -
#include "CustomLinkedList.h"
using namespace std;
int main()
{
CustomLinkedList<int> firstList;
firstList.add(32);
firstList.printlist();
//Pause the program until input is received
int i;
cin >> i;
return 0;
}
I get an error upon compilation however - error C2955: 'Node' : use of class template requires template argument list - which points me to the following line of code in my add method -
Node* temp = new Node<T>;
I do not understand why this has no information about the type, since it was passed to linked list when created in my driver class. What should I be doing to pass the type information to Node?
Should I create a private node struct instead of a seperate class, and combine the methods of both classes in one file? I'm not certain this would overcome the problem, but I think it might. I would rather have seperate classes if possible though.
Thanks, Andrew.
While the answers have already been provided, I think I'll add my grain of salt.
When designing templates class, it is a good idea not to repeat the template arguments just about everywhere, just in case you wish to (one day) change a particular detail. In general, this is done by using typedefs.
template <class T>
class Node
{
public:
// bunch of types
typedef T value_type;
typedef T& reference_type;
typedef T const& const_reference_type;
typedef T* pointer_type;
typedef T const* const_pointer_type;
// From now on, T should never appear
private:
value_type m_value;
Node* m_next;
};
template <class T>
class List
{
// private, no need to expose implementation
typedef Node<T> node_type;
// From now on, T should never appear
typedef node_type* node_pointer;
public:
typedef typename node_type::value_type value_type;
typedef typename node_type::reference_type reference_type;
typedef typename node_type::const_reference_type const_reference_type;
// ...
void add(value_type info);
private:
node_pointer m_head, m_tail;
};
It is also better to define the methods outside of the class declaration, makes it is easier to read the interface.
template <class T>
void List<T>::add(value_type info)
{
if(head == NULL) //if our list is currently empty
{
head = new node_type;
head->setData(info);
tail = head;
}
else //if not empty add to the end and move the tail
{
Node* temp = new node_type;
temp->setData(info);
temp->setNextNull();
tail->setNext(temp);
tail = tail->getNext();
}
}
Now, a couple of remarks:
it would be more user friendly if List<T>::add was returning an iterator to the newly added objects, like insert methods do in the STL (and you could rename it insert too)
in the implementation of List<T>::add you assign memory to temp then perform a bunch of operations, if any throws, you have leaked memory
the setNextNull call should not be necessary: the constructor of Node should initialize all the data member to meaningfull values, included m_next
So here is a revised version:
template <class T>
Node<T>::Node(value_type info): m_value(info), m_next(NULL) {}
template <class T>
typename List<T>::iterator insert(value_type info)
{
if (m_head == NULL)
{
m_head = new node_type(info);
m_tail = m_head;
return iterator(m_tail);
}
else
{
m_tail.setNext(new node_type(info));
node_pointer temp = m_tail;
m_tail = temp.getNext();
return iterator(temp);
}
}
Note how the simple fact of using a proper constructor improves our exception safety: if ever anything throw during the constructor, new is required not to allocate any memory, thus nothing is leaked and we have not performed any operation yet. Our List<T>::insert method is now resilient.
Final question:
Usual insert methods of single linked lists insert at the beginning, because it's easier:
template <class T>
typename List<T>::iterator insert(value_type info)
{
m_head = new node_type(info, m_head); // if this throws, m_head is left unmodified
return iterator(m_head);
}
Are you sure you want to go with an insert at the end ? or did you do it this way because of the push_back method on traditional vectors and lists ?
Might wanna try
Node<T>* temp = new Node<T>;
Also, to get hints on how to design the list, you can of course look at std::list, although it can be a bit daunting at times.
You need:
Node<T> *temp = new Node<T>;
Might be worth a typedef NodeType = Node<T> in the CustomLinkedList class to prevent this problem from cropping up again.
That line should read
Node<T>* temp = new Node<T>;
Same for the next pointer in the Node class.
As said, the solution is
Node<T>* temp = new Node<T>;
... because Node itself is not a type, Node<T> is.
And you will need to specify the template parameter for the Node *temp in printlist also.
// file: main.cc
#include "linkedlist.h"
int main(int argc, char *argv[]) {
LinkedList<int> list;
for(int i = 1; i < 10; i++) list.add(i);
list.print();
}
// file: node.h
#ifndef _NODE_H
#define _NODE_H
template<typename T> class LinkedList;
template<typename T>class Node {
friend class LinkedList<T>;
public:
Node(T data = 0, Node<T> *next = 0)
: data(data), next(next)
{ /* vacio */ }
private:
T data;
Node<T> *next;
};
#endif//_NODE_H
// file: linkedlist.h
#ifndef _LINKEDLIST_H
#define _LINKEDLIST_H
#include <iostream>
using namespace std;
#include "node.h"
template<typename T> class LinkedList {
public:
LinkedList();
~LinkedList();
void add(T);
void print();
private:
Node<T> *head;
Node<T> *tail;
};
#endif//_LINKEDLIST_H
template<typename T>LinkedList<T>::LinkedList()
: head(0), tail(0)
{ /* empty */ }
template<typename T>LinkedList<T>::~LinkedList() {
if(head) {
Node<T> *p = head;
Node<T> *q = 0;
while(p) {
q = p;
p = p->next;
delete q;
}
cout << endl;
}
}
template<typename T>LinkedList<T>::void add(T info) {
if(head) {
tail->next = new Node<T>(info);
tail = tail->next;
} else {
head = tail = new Node<T>(info);
}
}
template<typename T>LinkedList<T>::void print() {
if(head) {
Node<T> *p = head;
while(p) {
cout << p->data << "-> ";
p = p->next;
}
cout << endl;
}
}
You Should add new node in this way
Node<T>* temp=new node<T>;
Hope you Solved :)
#include<iostream>
using namespace std;
template < class data > class node {
private :
data t;
node<data > *ptr;
public:
node() {
ptr = NULL;
}
data get_data() {
return t;
}
void set_data(data d) {
t = d;
}
void set_ptr(node<data > *p) {
ptr = p;
}
node * get_ptr() {
return ptr;
}
};
template <class data > node < data > * add_at_last(data d , node<data > *start) {
node< data > *temp , *p = start;
temp = new node<data>();
temp->set_data(d);
temp->set_ptr(NULL);
if(!start) {
start = temp;
return temp;
}
else {
while(p->get_ptr()) {
p = p->get_ptr();
}
p->set_ptr(temp);
}
}
template < class data > void display(node< data > *start) {
node< data > *temp;
temp = start;
while(temp != NULL) {
cout<<temp->get_data()<<" ";
temp = temp->get_ptr();
}
cout<<endl;
}
template <class data > node < data > * reverse_list(node<data > * start) {
node< data > *p = start , *q = NULL , *r = NULL;
while(p->get_ptr()) {
q = p;
p = p->get_ptr();
q->set_ptr(r);
r = q;
}
p->set_ptr(r);
return p;
}
int main() {
node < int > *start;
for(int i =0 ; i < 10 ; i ++) {
if(!i) {
start = add_at_last(i , start);
}
else {
add_at_last(i , start);
}
}
display(start);
start = reverse_list(start);
cout<<endl<<"reverse list is"<<endl<<endl;
display(start);
}