Given the mapping a = 1, b = 2, ... z = 26, and an encoded message, count the number of ways it can be decoded.
Examples:
>>> coding_problem_07('111') # possible interpretations: 'aaa', 'ka', 'ak'
3
>>> coding_problem_07('2626') # 'zz', 'zbf', 'bfz', 'bfbf'
4