Question

Suppose we implement a doubly linked list class template LinkedList with template type T. LinkedList has fields Node *headPtr, Node *tailPtr and int length, where the struct type Node has fields prev and next of type Node* along with data of type T. The prev and next pointers of each Node points to the previous and next Nodes in the list (or are respectively null in the case of the list’s head or tail node).

We wish to detect "invalid" binary trees in which there is a loop from some node back to itself. Write a function

bool hasALoop(Node * r);

that returns true if the tree with root r has such a loop.

Answer 1

ANSWER

bool hasALoop(Node *r)

{

Node *pl=r, *pr=r; //two nodes to check loop left and right

bool b=false;

//to check loop left side of Node r

while(pl !=NULL)
{
if(pl==r) // if there is any Node that is same as r i.e there is a loop
{
b=true; //then we change Boolean value to true and break loop
break;
}

b=hasALoop(pl); //to check whether at any other node pl, there is a loop or not

if(b==true)

break;

pl=pl->pre; //to go to previous Node of pl
}

//to check loop right side of Node r
while(pr !=NULL)
{
if(pr==r) // Similarly, if there is any Node that is same as r i.e there is a loop
{
b=true; //then we change Boolean value to true and break loop
break;
}

b=hasALoop(pr); //Similarly here also, we check loop at every node

if(b==true)

break;
pr=pr->next; //to go to next Node of pl
}

return b; //finally return boolean value
}//end of function