A math puzzle has a form such as 2BCD+BCDE=DA01. We want to find a solution, where A, B, C, D are distinct digits, different from any digits in the puzzle. Here, a solution is 2345+3456=5801. In general, a puzzle can have any combination of up to ten digits and numbers.

Write a recursive method for computing the solutions to such a puzzle.

Draft: Just complete the Puzzle class—no recursion yet. It should pass the tester.