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Finding a loop in a linked List

Finding a loop in a linked List:-

public class LinkedListLoop {

 //Two pointers
 public Node loopCheck(Node head)
 {
  //fast pointer take two steps at a time
  Node fastptr=head;
  //slow pointer take one step at a time
  Node slowptr=head;
  
  if(head==null)
  {
   System.out.println("no loops empty list");
  }
  
  //Till any pointer becomes null
  while(slowptr!=null && fastptr!=null && fastptr.next!=null)
  {
   slowptr=slowptr.next;
   fastptr=fastptr.next.next;
   
   //if both pointers point to same node
   //possible only in loop list
   if(slowptr==fastptr)
   {
    System.out.println("loopfound");
    fastptr=head;
    while(fastptr.next!=slowptr)
    {
     fastptr=fastptr.next;
    }
     return fastptr;
   }
  }
  System.out.println("loop not found");
   return head;
 }
 
 public void makeCycle(Node head)
 {
  Node temp=head;
  while(temp.next.next!=null)
  {
   temp=temp.next;
  }
  temp.next=head.next.next;
 }
 
 
}

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Deleting a Node by passing data in LInkedList

Deleting a Node by passing data in LInkedList:-

The node can be deleted by passing the data value in a function.Here we have three pointers one to traverse the list other to point current node and third one to point previous of current node.



//deleting a given keypublic Node deleteKeyNode(Node head,int key){//traverse pointer Node temp=head;//previous pointer Node prevtemp=temp;while(temp!=null){//when key is at head positionif(key==head.data){ head=head.next; System.out.println("head is deleted");return head;}//when key is at any position other than headif(temp.data==key){ prevtemp.next=temp.next; temp.next=null; temp=prevtemp;} prevtemp=temp; temp=temp.next;}return head;}