Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself. This question is based on basic Linked List opreation ...

//Runtime: 32 ms, faster than 79.81% of C++ online submissions for Add Two Numbers. //Memory Usage: 71.1 MB, less than 26.28% of C++ online submissions for Add Two Numbers.