UNB/ CS/ David Bremner/ teaching/ cs2613/ books/ diveintopython3/ examples/ alphametics.py
'''Find solutions to alphametic equations.

>>> alphametics.solve('SEND + MORE == MONEY')
'9567 + 1085 == 10652'
'''

import re
import itertools

def solve(puzzle):
    words = re.findall('[A-Z]+', puzzle.upper())
    unique_characters = set(''.join(words))
    assert len(unique_characters) <= 10, 'Too many letters'
    first_letters = {word[0] for word in words}
    n = len(first_letters)
    sorted_characters = ''.join(first_letters) + \
        ''.join(unique_characters - first_letters)
    characters = tuple(ord(c) for c in sorted_characters)
    digits = tuple(ord(c) for c in '0123456789')
    zero = digits[0]
    for guess in itertools.permutations(digits, len(characters)):
        if zero not in guess[:n]:
            equation = puzzle.translate(dict(zip(characters, guess)))
            if eval(equation):
                return equation

if __name__ == '__main__':
    import sys
    for puzzle in sys.argv[1:]:
        print(puzzle)
        solution = solve(puzzle)
        if solution:
            print(solution)

# Copyright (c) 2009, Raymond Hettinger, All rights reserved.
# Ported to Python 3 and modified by Mark Pilgrim
# original: http://code.activestate.com/recipes/576615/
# 
# Redistribution and use in source and binary forms, with or without modification,
# are permitted provided that the following conditions are met:
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# * Redistributions of source code must retain the above copyright notice,
#   this list of conditions and the following disclaimer.
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 'AS IS'
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# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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