'''
You have two numbers represented by a linked list, where each node contains a single digit. The digits are stored in reverse order, such that the 1's digit is at the head of the list. Write a function that adds the two numbers and returns the sum as a linked list.

Example :
    Input: (7->1->6) + (5->9->2). That is, 617 + 295
    Output: 9->1->2. That is, 912.

Hints: 7, 30, 71, 95, 109
'''


def sum_lists(s):
    ''' '''
    pass

if __name__ == '__main__':
    assert sum_lists('') ==
    assert sum_lists('') ==
    assert sum_lists('') ==
    assert sum_lists('') ==
    assert sum_lists('') ==
