aoc2024day7.py

# === Parsing ===

equations = []
with open("input.txt", "r") as f:
    for line in f:
        target, _, operands = line.partition(":")
        equations.append(
            (
                int(target),
                [int(num) for num in operands.split()],
            )
        )

print(equations)
print(equations[-1])


# === Part 1 ===
from itertools import product
from operator import add, mul

operator_options = [add, mul]

total = 0
for target, operands in equations:
    all_operator_combinations = product(
        operator_options,
        repeat=len(operands) - 1,
    )
    for operator_combination in all_operator_combinations:
        partial_result = operands[0]
        for operand, operator in zip(operands[1:], operator_combination):
            partial_result = operator(partial_result, operand)
        if partial_result == target:
            total += target
            break

print(total)


# === Part 2 ===
from itertools import product
from operator import add, mul

operator_options = [
    add,
    mul,
    lambda x, y: int(f"{x}{y}"),
]


import time

""" 
start = time.perf_counter()

total = 0
for target, operands in equations:
    all_operator_combinations = product(
        operator_options,
        repeat=len(operands) - 1,
    )
    for operator_combination in all_operator_combinations:
        partial_result = operands[0]
        for operand, operator in zip(operands[1:], operator_combination):
            partial_result = operator(partial_result, operand)
        if partial_result == target:
            total += target
            break

end = time.perf_counter()
print(f"Got solution in {end - start}")
print(total)
 """

# === Part 2, take 2 ===
def is_valid(target, operands):
    if len(operands) == 1:
        return target == operands[0]
    elif not operands:
        return False

    last_op = operands[-1]
    tail = operands[:-1]

    if str(target).endswith(str(last_op)):  # concatenation
        if is_valid(target // pow(10, len(str(last_op))), tail):
            return True

    if target % last_op == 0:  # multiplication
        if is_valid(target // last_op, tail):
            return True

    if target > last_op:
        if is_valid(target - last_op, tail):  # addition
            return True

    return False


start = time.perf_counter()
total = 0
for target, operands in equations:
    if is_valid(target, operands):
        total += target
end = time.perf_counter()
print(f"Got solution in {end - start}")

print(total)