from itertools import combinations, permutations

def check_leading_zeros(*numbers):

return any(n[0] == '0' for n in numbers)

def test_equation(puzzle, substitutions):

equation = ''.join(substitutions.get(char) or char for char in puzzle)

left, right = equation.split(' == ')

left_numbers = left.split(' + ')

if check_leading_zeros(right, *left_numbers):

return False

return sum(map(int, left_numbers)) == int(right)

def solve(puzzle):

letters = set(char for char in puzzle if char.isupper())

numbers = map(str, range(10))

for c in combinations(numbers, len(letters)):

for p in permutations(c):

substitutions = dict(zip(letters, p))

if test_equation(puzzle, substitutions):

return {k: int(v) for k, v in substitutions.items()}

return {} # no solution found