Last Updated: 16 Oct, 2020

Easy

## Problem statement

#### You are given a singly Linked List of integers. Your task is to return true if the given singly linked list is a palindrome otherwise returns false.

##### For example:
``````The given linked list is 1 -> 2 -> 3 -> 2-> 1-> NULL.

It is a palindrome linked list because the given linked list has the same order of elements when traversed forwards and backward​.
``````
``````Can you solve the problem in O(N) time complexity and O(1) space complexity iteratively?
``````
##### Input format :
``````The first line of input contains an integer 'T' representing the number of test cases or queries to be processed. Then the test case follows.

The only line of each test case contains the elements of the singly linked list separated by a single space and terminated by -1. Hence, -1 would never be a list element.
``````
##### Output format :
``````For each test case, print “true” or “false” in a separate line.
``````
##### Note :
``````You do not need to print anything, it has already been taken care of. Just implement the given function.
``````
##### Constraints :
``````1 <= T <= 10
0 <= L <= 10^5
1 <= data <= 10^9 and data != -1

Where L is the number of nodes in the Linked List.

Time Limit: 1 sec
``````

## Approaches

### 01 Approach

1. The idea is to traverse the Linked List from head to tail and push every encountered node data into the stack.
2. Then we traverse the Linked List and for each node, we pop the top element from the stack and compare it with current node data of the Linked List. If they mismatch then the current linked list is not palindrome else if all elements match then the linked list is a palindrome.