My code is about detecting a loop / cycle in a linked list, and then removing the error. However, only the first element of the linked list is getting printed after running the code to remove the loop / cycle.
I have already tried merging the detectCycle() and removeCycle() functions, but it has no impact on the output.
class ListElem
{
public:
int value;
ListElem *next; //Pointer used to make link
};
int length(ListElem *head) //function to check length of linked list
{
int len = 0;
while(head != NULL)
{
head = head -> next;
len += 1;
}
return len;
}
void insertAtTail(ListElem *&head, ListElem *elem) //if the list is non - empty, the insertAtTail algorithm
//does not change the head of the list
{
ListElem *lastElem; //lastElem will point to the last element
if ( head == NULL ) // Detect and handle exception case.... (in case the list is empty)
{
head = elem;
elem->next = NULL;
}
else
{
lastElem = head;
while(lastElem->next != NULL) //Find the last element in the list
{
lastElem = lastElem->next;
}
lastElem->next = elem; // Link "elem" to lastElem:
elem->next = NULL; // Mark new elem as the last element:
}
}
void buildList(ListElem *&head)
{
int data; // data = the value of elements to be inserted in linked list that will be input by the user
cin>>data;
ListElem *p;
while (data != -1) // when the user inputs '-1', the process of taking input will stop
{
p = new ListElem;
p -> value = data;
insertAtTail(head, p);
cin>>data;
}
}
void Print(ListElem *head)
{
ListElem *p;
p = head; // Very important: start at first element
cout << "List ==> ";
while ( p != NULL )
{
cout << p->value << " "; // Access value stored in list element
p = p->next; // Visit next element in list
}
cout << "\n\n";
}
void removeCycle(ListElem *head, ListElem *fast)
{
ListElem *slow = head;
while(slow ->next != fast -> next) // ensures that slow pointer does not go past the fast pointer, and detects the
{ // node at which slow and fast pointers point to the same node
slow = slow -> next;
fast = fast -> next;
}
fast -> next = NULL; // This works when the end of the loop is reached and the “next” pointer to that node
//is made NULL representing the end of a linked list without loop
}
bool detectCycle(ListElem *head)
{
ListElem *slow = head;
ListElem *fast = head;
while(fast != NULL && fast -> next != NULL)
{
fast = fast -> next -> next;
slow = slow -> next;
if(fast == slow)
{
removeCycle(head, fast); // this will call the remove cycle function to remove the cycle. The position
// of the fast pointer is to be retained,
so it is passed as argument to the
return true; // remove cycle function
}
}
return false;
}
int main()
{
ListElem *head = NULL;
buildList(head);
/* Deliberately create a loop/cycle for testing */
head->next->next->next->next->next = head->next->next->next;
if(detectCycle(head))
{
cout<<"A loop was present, and has been removed. List after removal of loop is :"<<endl<<endl;
Print(head);
}
else
{
cout<<"A loop was not present"<<endl;
Print(head);
}
cout<<"The length of the list is : "<<length(head);
cout<<endl<<endl;
return 0;
}
I expect the Print() function to output the entire corrected list.
