Given two decimal numbers represented by two linked lists of size N and M respectively. The task is to return a linked list that represents the sum of these two numbers.

For example, the number 190 will be represented by the linked list, 1->9->0->null, similarly 25 by 2->5->null. Sum of these two numbers is 190 + 25 = 215, which will be represented by 2->1->5->null. You are required to return the head of the linked list 2->1->5->null.

Example 1:

Input:
N = 2
valueN[] = {4,5}
M = 3
valueM[] = {3,4,5}
Output: 3 9 0  
Explanation: For the given two linked
list (4 5) and (3 4 5), after adding
the two linked list resultant linked
list will be (3 9 0).

Example 2:

Input:
N = 2
valueN[] = {6,3}
M = 1
valueM[] = {7}
Output: 7 0
Explanation: For the given two linked
list (6 3) and (7), after adding the
two linked list resultant linked list
will be (7 0).

Your Task:
The task is to complete the function addTwoLists() which has node reference of both the linked lists and returns the head of the sum list.

Expected Time Complexity: O(N+M)
Expected Auxiliary Space: O(Max(N,M)) for the resultant list.

Constraints:
1 <= N, M <= 5000