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Author: adityajamwal02

CheckIfLinkedListIsPalindrome.cpp

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+/*
+Given a singly linked list of size N of integers. The task is to check if the given linked list is palindrome or not.
+
+Example 1:
+Input:
+N = 3
+value[] = {1,2,1}
+Output: 1
+Explanation: The given linked list is
+1 2 1 , which is a palindrome and
+Hence, the output is 1.
+
+Example 2:
+Input:
+N = 4
+value[] = {1,2,3,4}
+Output: 0
+Explanation: The given linked list
+is 1 2 3 4 , which is not a palindrome
+and Hence, the output is 0.
+Your Task:
+The task is to complete the function isPalindrome() which takes head as reference as the only parameter and returns true or false if linked list is palindrome or not respectively.
+
+Expected Time Complexity: O(N)
+Expected Auxialliary Space Usage: O(1)  (ie, you should not use the recursive stack space as well)
+*/
+
+/// No Linear Extra Space
+
+class Solution{
+  public:
+    //Function to reverse the LL
+    Node* makeReverse(Node *head){
+        if(!head or !head->next) return head;
+        Node *reverse=makeReverse(head->next);
+        head->next->next=head;
+        head->next=NULL;
+    return reverse;
+    }
+
+    //Function to check whether the list is palindrome.
+    bool isPalindrome(Node *head)
+    {
+        if(!head or !head->next) return true;
+        Node *slow=head;
+        Node *fast=head->next;
+        while(fast and fast->next){
+            slow=slow->next;
+            fast=fast->next->next;
+        }
+        Node *reverse=makeReverse(slow->next);
+        slow=head;
+        while(slow and reverse){
+            if(slow->data!=reverse->data) return false;
+            slow=slow->next;
+            reverse=reverse->next;
+        }
+    return true;
+    }
+};