Detect and remove Loop in LL

public static int DetectRemove(LinkedList head){

  LinkedList slow = head,fast=head;

  if(head==null)

   return 0;

  while(slow != null &&  fast !=null && fast.next!=null){

   slow=slow.next;

   fast=fast.next.next;

   if(slow.value == fast.value){

    removeLoop(slow,head);

    return 1;

   }

  }

  return 0;

 }

 

 

 public static void removeLoop(LinkedList loopNode , LinkedList head) {

  // First find out the length of the loop

  int loopLength =1;

  LinkedList loopNodeCopy = loopNode;

  while(loopNodeCopy.next.value!= loopNode.value){

   loopNodeCopy = loopNodeCopy.next;

   loopLength++;

  }

  System.out.println("Loop Length :" + loopLength);

  

  LinkedList ptrToHead = head;

  LinkedList ptrToKth  = head;

  

  //Move one pointer to Kth node

  int k = 0;

  while(k<loopLength) {

   ptrToKth = ptrToKth.next;

   k++;

  }

  System.out.println("Kth node:" + ptrToKth.value);

  

  // Increment both pointers(from head and one frm Kth node)

  // prev to keep track of the last node in d loop

  LinkedList prev = null;

  while (ptrToHead.value != ptrToKth.value){

   prev=ptrToKth;

   ptrToHead = ptrToHead.next;

   ptrToKth  = ptrToKth.next;

  }

  prev.next=null;

  

  LinkedList.Display(head);

 }

Reverse alternate k grp of nodes

public static LinkedList reverseK(LinkedList head, int k){
LinkedList prev = null,next=null;
LinkedList curr = head;
int count = 0;
while (curr !=null && count < k) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
count++;
}
if(head!=null)
head.next = curr;
count = 0;
while(curr!=null && count < k-1){
curr = curr.next;
count++;
}

    if(curr!=null)
curr.next = reverseK(curr.next,k);
return prev;
}

Reverse in group of size K

public static LinkedList reverseK(LinkedList head, int k){
LinkedList prev = null,next=null;
LinkedList curr = head;
int count = 0;
while (curr !=null && count < k) {
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
count++;
}

if(next!=null)
head.next = reverseK(next,k);
return prev;
}

Delete nodes which have a greater value on right side

public static LinkedList DeleteRight(LinkedList node){
if(node==null)
return null;
LinkedList prev = null;
LinkedList head = node;
int max = 0;
while(node!=null) {
if(max < node.value){
max = node.value;
prev = node;

}
else
prev.next = node.next;
node=node.next;
}
return head;
}

Pairwise swap of elements

public static LinkedList pairSwap(LinkedList head) {
int temp;
LinkedList start = head;
if(head==null)
return null;
else{
while(head!=null && head.next!=null){
temp = head.value;
head.value = head.next.value;
head.next.value = temp;
head = head.next.next;

}
return start;
}

Addition Linked list !

public static void Add(LinkedList num1, LinkedList num2) {
LinkedList result=null,curr=null,currLast=null;
int carry=0;
while(num1!=null || num2 !=null){
int sum = 0;
sum = carry + (num1!=null?num1.value:0) + (num2!=null?num2.value:0);
carry = sum>=10?1:0;
sum = sum%10;

//new node with sum
currLast = new LinkedList(sum);
//first node : make head to this
if(result==null)
  result = currLast;
//else connect to curr next
else
curr.next = currLast;
curr = currLast;
if(num1!=null)
num1 = num1.next;
if(num2!=null)
   num2 = num2.next;
}
if(carry > 0)
curr.next = new LinkedList(carry);

}

Reverse a linked list iterative n recursive

  public static RevLinkedList reverse(RevLinkedList p){
   
    if(p.next==null){
      return p;
    }
    RevLinkedList q=reverse(p.next);
    p.next.next=p;
    p.next=null;
    return q;
  }

Iterative :


    public static void reverse(Iterative_reversal p){
      Iterative_reversal curr=p.next;
      Iterative_reversal head=p;
      Iterative_reversal temp=null;
      Iterative_reversal prev=p;
      while(curr.next!=null)
      {
        temp=curr.next;
        curr.next=prev;
        prev=curr;
        curr=temp;
      }
      curr.next=prev;
      head.next=null;
      Display(curr);
     
     
    }

Nth node from end of a linked list

public static void Nth(LinkedList node, int k){
 
LinkedList curr = node ,temp = node;
if(node == null )
return;
while(--k!=0){

if(temp.next!=null)
 temp=temp.next;
else{
System.out.println("Less no of nodes");
   return;
}
}
while(temp.next!=null){
temp = temp.next;
curr=curr.next;
}
System.out.println(curr.value);
}

Deleting a node from linked list

   public static void delete(LinkedList node, int value){
if(node == null)
  return;
while(node!=null){
if(node.value == value){
node.value=node.next.value;
node.next=node.next.next;
}
else
node = node.next;
}
}