def test_build_2_greedy():
replacements, _ = parse_input(build_replacements)
n_steps = build_molecule(replacements, 'HOHOHO', reverse=True, greedy=True)
assert n_steps == 6
def test_build_2():
replacements, _ = parse_input(build_replacements)
n_steps = build_molecule(replacements, 'HOHOHO')
assert n_steps == 6
def test_build_1_reverse():
replacements, _ = parse_input(build_replacements)
n_steps = build_molecule(replacements, 'HOH', reverse=True)
assert n_steps == 3
def test_part_2():
with open('input.txt') as f:
specs = f.read()
replacements, molecule = parse_input(specs)
n_steps = build_molecule(replacements, target=molecule, reverse=True, greedy=True)
assert n_steps == 212