Add First and Second Reversed Half

You have been given a Linked List of 'N' nodes such that each node represents a single digit.

Your task is to return a node 'X', where 'X' represents the head of the Linked List storing the digits of the sum(most significant digit at the head) formed by adding 1st half and reverse of 2nd half of the given linked list.

Note:

1. When 'N' is odd consider the middle element to be part of 1st half.
2. The sum should not contain any leading zero, except the number 0 itself.

For example:

Given a Linked List: 1-2-3-4-5-5-6

First half: 1-2-3-4   
Reversed second half: 6-5-5

Output linkedlist: 1-8-8-9 = (1234 + 655 = 1889)

Follow Up:

Can you add both halves without finding the length of LinkedList and in O(1) space?

Input format :

A single line of input contains the elements of the singly linked list separated by a single space and terminated by -1.

Output format :

For each input, print a single line containing a string denoting the required sum.

Note:

You do not need to print anything; it has already been taken care of. Just implement the given function.

Constraints :

0 <= 'N' <= 10 ^ 5
0 <= 'DATA' <= 9

Where 'N' is the number of nodes in linked list and 'DATA' is the integer value in each node.

Time Limit: 1 sec

Sample Input 1:

1 2 4 5 6 -1

Sample Output 1:

189

Explanation for Sample Input 1:

The first half of the given linkedlist is: 1-2-4
The second half of the given linkedlist is: 6-5
Sum of both parts = 124 + 65 = 189

Sample Input 2:

3 9 0 1 1 0 -1

Sample Output 2:

401