// C++ program to check if a linked list with // loop is palindrome or not. #include   using namespace std; /* Link list node */ struct Node {  int data;  struct Node * next; }; /* Function to find loop starting node. loop_node --> Pointer to one of the loop nodes head --> Pointer to the start node of the linked list */ Node* getLoopstart(Node *loop_node Node *head) {  Node *ptr1 = loop_node;  Node *ptr2 = loop_node;  // Count the number of nodes in loop  unsigned int k = 1 i;  while (ptr1->next != ptr2)  {  ptr1 = ptr1->next;  k++;  }  // Fix one pointer to head  ptr1 = head;  // And the other pointer to k nodes after head  ptr2 = head;  for (i = 0; i < k; i++)  ptr2 = ptr2->next;  /* Move both pointers at the same pace  they will meet at loop starting node */  while (ptr2 != ptr1)  {  ptr1 = ptr1->next;  ptr2 = ptr2->next;  }  return ptr1; } /* This function detects and find loop starting  node in the list*/ Node* detectAndgetLoopstarting(Node *head) {  Node *slow_p = head *fast_p = head*loop_start;  //Start traversing list and detect loop  while (slow_p && fast_p && fast_p->next)  {  slow_p = slow_p->next;  fast_p = fast_p->next->next;  /* If slow_p and fast_p meet then find  the loop starting node*/  if (slow_p == fast_p)  {  loop_start = getLoopstart(slow_p head);  break;  }  }  // Return starting node of loop  return loop_start; } // Utility function to check if a linked list with loop // is palindrome with given starting point. bool isPalindromeUtil(Node *head Node* loop_start) {  Node *ptr = head;  stack<int> s;  // Traverse linked list until last node is equal  // to loop_start and store the elements till start  // in a stack  int count = 0;  while (ptr != loop_start || count != 1)  {  s.push(ptr->data);  if (ptr == loop_start)  count = 1;  ptr = ptr->next;  }  ptr = head;  count = 0;  // Traverse linked list until last node is  // equal to loop_start second time  while (ptr != loop_start || count != 1)  {  // Compare data of node with the top of stack  // If equal then continue  if (ptr->data == s.top())  s.pop();  // Else return false  else  return false;  if (ptr == loop_start)  count = 1;  ptr = ptr->next;  }  // Return true if linked list is palindrome  return true; } // Function to find if linked list is palindrome or not bool isPalindrome(Node* head) {  // Find the loop starting node  Node* loop_start = detectAndgetLoopstarting(head);  // Check if linked list is palindrome  return isPalindromeUtil(head loop_start); } Node *newNode(int key) {  Node *temp = new Node;  temp->data = key;  temp->next = NULL;  return temp; } /* Driver program to test above function*/ int main() {  Node *head = newNode(50);  head->next = newNode(20);  head->next->next = newNode(15);  head->next->next->next = newNode(20);  head->next->next->next->next = newNode(50);  /* Create a loop for testing */  head->next->next->next->next->next = head->next->next;  isPalindrome(head)? cout << 'nPalindrome'  : cout << 'nNot Palindrome';  return 0; } 

// Java program to check if a linked list // with loop is palindrome or not. import java.util.*; class GfG  { /* Link list node */ static class Node  {   int data;   Node next;  } /* Function to find loop starting node.  loop_node --> Pointer to one of  the loop nodes head --> Pointer to  the start node of the linked list */ static Node getLoopstart(Node loop_node   Node head)  {   Node ptr1 = loop_node;   Node ptr2 = loop_node;   // Count the number of nodes in loop   int k = 1 i;   while (ptr1.next != ptr2)   {   ptr1 = ptr1.next;   k++;   }   // Fix one pointer to head   ptr1 = head;   // And the other pointer to k   // nodes after head   ptr2 = head;   for (i = 0; i < k; i++)   ptr2 = ptr2.next;   /* Move both pointers at the same pace   they will meet at loop starting node */  while (ptr2 != ptr1)   {   ptr1 = ptr1.next;   ptr2 = ptr2.next;   }   return ptr1;  }  /* This function detects and find  loop starting node in the list*/ static Node detectAndgetLoopstarting(Node head)  {   Node slow_p = head fast_p = headloop_start = null;   //Start traversing list and detect loop   while (slow_p != null && fast_p != null &&   fast_p.next != null)   {   slow_p = slow_p.next;   fast_p = fast_p.next.next;   /* If slow_p and fast_p meet then find   the loop starting node*/  if (slow_p == fast_p)   {   loop_start = getLoopstart(slow_p head);   break;   }   }   // Return starting node of loop   return loop_start;  }  // Utility function to check if  // a linked list with loop is  // palindrome with given starting point.  static boolean isPalindromeUtil(Node head  Node loop_start)  {   Node ptr = head;   Stack<Integer> s = new Stack<Integer> ();   // Traverse linked list until last node   // is equal to loop_start and store the   // elements till start in a stack   int count = 0;   while (ptr != loop_start || count != 1)   {   s.push(ptr.data);   if (ptr == loop_start)   count = 1;   ptr = ptr.next;   }   ptr = head;   count = 0;   // Traverse linked list until last node is   // equal to loop_start second time   while (ptr != loop_start || count != 1)   {   // Compare data of node with the top of stack   // If equal then continue   if (ptr.data == s.peek())   s.pop();   // Else return false   else  return false;   if (ptr == loop_start)   count = 1;   ptr = ptr.next;   }   // Return true if linked list is palindrome   return true;  }  // Function to find if linked list // is palindrome or not  static boolean isPalindrome(Node head)  {   // Find the loop starting node   Node loop_start = detectAndgetLoopstarting(head);   // Check if linked list is palindrome   return isPalindromeUtil(head loop_start);  }  static Node newNode(int key)  {   Node temp = new Node();   temp.data = key;   temp.next = null;   return temp;  }  /* Driver code*/ public static void main(String[] args)  {   Node head = newNode(50);   head.next = newNode(20);   head.next.next = newNode(15);   head.next.next.next = newNode(20);   head.next.next.next.next = newNode(50);   /* Create a loop for testing */  head.next.next.next.next.next = head.next.next;   if(isPalindrome(head) == true)  System.out.println('Palindrome');  else  System.out.println('Not Palindrome');  } }  // This code is contributed by prerna saini 

# Python3 program to check if a linked list # with loop is palindrome or not. # Node class  class Node: # Constructor to initialize the node object  def __init__(self data): self.data = data self.next = None # Function to find loop starting node.  # loop_node -. Pointer to one of  # the loop nodes head -. Pointer to  # the start node of the linked list def getLoopstart(loop_nodehead): ptr1 = loop_node ptr2 = loop_node # Count the number of nodes in loop  k = 1 i = 0 while (ptr1.next != ptr2): ptr1 = ptr1.next k = k + 1 # Fix one pointer to head  ptr1 = head # And the other pointer to k  # nodes after head  ptr2 = head i = 0 while ( i < k ) : ptr2 = ptr2.next i = i + 1 # Move both pointers at the same pace  #they will meet at loop starting node */ while (ptr2 != ptr1): ptr1 = ptr1.next ptr2 = ptr2.next return ptr1 # This function detects and find  # loop starting node in the list def detectAndgetLoopstarting(head): slow_p = head fast_p = head loop_start = None # Start traversing list and detect loop  while (slow_p != None and fast_p != None and fast_p.next != None) : slow_p = slow_p.next fast_p = fast_p.next.next # If slow_p and fast_p meet then find  # the loop starting node if (slow_p == fast_p) : loop_start = getLoopstart(slow_p head) break # Return starting node of loop  return loop_start # Utility function to check if  # a linked list with loop is  # palindrome with given starting point.  def isPalindromeUtil(head loop_start): ptr = head s = [] # Traverse linked list until last node  # is equal to loop_start and store the  # elements till start in a stack  count = 0 while (ptr != loop_start or count != 1): s.append(ptr.data) if (ptr == loop_start) : count = 1 ptr = ptr.next ptr = head count = 0 # Traverse linked list until last node is  # equal to loop_start second time  while (ptr != loop_start or count != 1): # Compare data of node with the top of stack  # If equal then continue  if (ptr.data == s[-1]): s.pop() # Else return False  else: return False if (ptr == loop_start) : count = 1 ptr = ptr.next # Return True if linked list is palindrome  return True # Function to find if linked list # is palindrome or not  def isPalindrome(head) : # Find the loop starting node  loop_start = detectAndgetLoopstarting(head) # Check if linked list is palindrome  return isPalindromeUtil(head loop_start) def newNode(key) : temp = Node(0) temp.data = key temp.next = None return temp # Driver code head = newNode(50) head.next = newNode(20) head.next.next = newNode(15) head.next.next.next = newNode(20) head.next.next.next.next = newNode(50) # Create a loop for testing  head.next.next.next.next.next = head.next.next if(isPalindrome(head) == True): print('Palindrome') else: print('Not Palindrome') # This code is contributed by Arnab Kundu 

// C# program to check if a linked list // with loop is palindrome or not. using System; using System.Collections.Generic;  class GfG  { /* Link list node */ class Node  {   public int data;   public Node next;  } /* Function to find loop starting node.  loop_node --> Pointer to one of  the loop nodes head --> Pointer to  the start node of the linked list */ static Node getLoopstart(Node loop_node   Node head)  {   Node ptr1 = loop_node;   Node ptr2 = loop_node;   // Count the number of nodes in loop   int k = 1 i;   while (ptr1.next != ptr2)   {   ptr1 = ptr1.next;   k++;   }   // Fix one pointer to head   ptr1 = head;   // And the other pointer to k   // nodes after head   ptr2 = head;   for (i = 0; i < k; i++)   ptr2 = ptr2.next;   /* Move both pointers at the same pace   they will meet at loop starting node */  while (ptr2 != ptr1)   {   ptr1 = ptr1.next;   ptr2 = ptr2.next;   }   return ptr1;  }  /* This function detects and find  loop starting node in the list*/ static Node detectAndgetLoopstarting(Node head)  {   Node slow_p = head fast_p = headloop_start = null;   //Start traversing list and detect loop   while (slow_p != null && fast_p != null &&   fast_p.next != null)   {   slow_p = slow_p.next;   fast_p = fast_p.next.next;   /* If slow_p and fast_p meet then find   the loop starting node*/  if (slow_p == fast_p)   {   loop_start = getLoopstart(slow_p head);   break;   }   }   // Return starting node of loop   return loop_start;  }  // Utility function to check if  // a linked list with loop is  // palindrome with given starting point.  static bool isPalindromeUtil(Node head  Node loop_start)  {   Node ptr = head;   Stack<int> s = new Stack<int> ();   // Traverse linked list until last node   // is equal to loop_start and store the   // elements till start in a stack   int count = 0;   while (ptr != loop_start || count != 1)   {   s.Push(ptr.data);   if (ptr == loop_start)   count = 1;   ptr = ptr.next;   }   ptr = head;   count = 0;   // Traverse linked list until last node is   // equal to loop_start second time   while (ptr != loop_start || count != 1)   {   // Compare data of node with the top of stack   // If equal then continue   if (ptr.data == s.Peek())   s.Pop();   // Else return false   else  return false;   if (ptr == loop_start)   count = 1;   ptr = ptr.next;   }   // Return true if linked list is palindrome   return true;  }  // Function to find if linked list // is palindrome or not  static bool isPalindrome(Node head)  {   // Find the loop starting node   Node loop_start = detectAndgetLoopstarting(head);   // Check if linked list is palindrome   return isPalindromeUtil(head loop_start);  }  static Node newNode(int key)  {   Node temp = new Node();   temp.data = key;   temp.next = null;   return temp;  }  /* Driver code*/ public static void Main(String[] args)  {   Node head = newNode(50);   head.next = newNode(20);   head.next.next = newNode(15);   head.next.next.next = newNode(20);   head.next.next.next.next = newNode(50);   /* Create a loop for testing */  head.next.next.next.next.next = head.next.next;   if(isPalindrome(head) == true)  Console.WriteLine('Palindrome');  else  Console.WriteLine('Not Palindrome');  } } /* This code is contributed by 29AjayKumar */ 

<script> // javascript program to check if a linked list // with loop is palindrome or not.class GfG {  /* Link list node */  class Node {  constructor() {  this.data = 0;  this.next = null;  }  }  /*  * Function to find loop starting node. loop_node --> Pointer to one of the loop  * nodes head --> Pointer to the start node of the linked list  */  function getLoopstart(loop_node head) {  var ptr1 = loop_node;  var ptr2 = loop_node;  // Count the number of nodes in loop  var k = 1 i;  while (ptr1.next != ptr2) {  ptr1 = ptr1.next;  k++;  }  // Fix one pointer to head  ptr1 = head;  // And the other pointer to k  // nodes after head  ptr2 = head;  for (i = 0; i < k; i++)  ptr2 = ptr2.next;  /*  * Move both pointers at the same pace they will meet at loop starting node  */  while (ptr2 != ptr1) {  ptr1 = ptr1.next;  ptr2 = ptr2.next;  }  return ptr1;  }  /*  * This function detects and find loop starting node in the list  */  function detectAndgetLoopstarting(head) {  var slow_p = head fast_p = head loop_start = null;  // Start traversing list and detect loop  while (slow_p != null && fast_p != null && fast_p.next != null) {  slow_p = slow_p.next;  fast_p = fast_p.next.next;  /*  * If slow_p and fast_p meet then find the loop starting node  */  if (slow_p == fast_p) {  loop_start = getLoopstart(slow_p head);  break;  }  }  // Return starting node of loop  return loop_start;  }  // Utility function to check if  // a linked list with loop is  // palindrome with given starting point.  function isPalindromeUtil(head loop_start) {  var ptr = head;  var s = [];  // Traverse linked list until last node  // is equal to loop_start and store the  // elements till start in a stack  var count = 0;  while (ptr != loop_start || count != 1) {  s.push(ptr.data);  if (ptr == loop_start)  count = 1;  ptr = ptr.next;  }  ptr = head;  count = 0;  // Traverse linked list until last node is  // equal to loop_start second time  while (ptr != loop_start || count != 1) {  // Compare data of node with the top of stack  // If equal then continue  var stk = s.pop();  if (ptr.data == stk);    // Else return false  else{  s.push(stk);  return false;  }  if (ptr == loop_start)  count = 1;  ptr = ptr.next;  }  // Return true if linked list is palindrome  return true;  }  // Function to find if linked list  // is palindrome or not  function isPalindrome(head) {  // Find the loop starting node  var loop_start = detectAndgetLoopstarting(head);  // Check if linked list is palindrome  return isPalindromeUtil(head loop_start);  }  function newNode(key) {  var temp = new Node();  temp.data = key;  temp.next = null;  return temp;  }  /* Driver code */    var head = newNode(50);  head.next = newNode(20);  head.next.next = newNode(15);  head.next.next.next = newNode(20);  head.next.next.next.next = newNode(50);  /* Create a loop for testing */  head.next.next.next.next.next = head.next.next;  if (isPalindrome(head) == true)  document.write('Palindrome');  else  document.write('Not Palindrome'); // This code contributed by aashish1995  </script>