This problem was asked by Microsoft.
Let's represent an integer in a linked list format by having each node represent a digit in the number. The nodes make up the number in reversed order.
For example, the following linked list:
1 -> 2 -> 3 -> 4 -> 5
is the number 54321.
Given two linked lists in this format, return their sum in the same linked list format.
For example, given
9 -> 9
5 -> 2
return 124 (99 + 25) as:
4 -> 2 -> 1