25.py

"""--- Day 25: Clock Signal ---"""

def solve(instructions, registers):

    # intialise program counter to zero
    cnt = 0
    # initialise blank transmission
    transmission = []

    while cnt < len(instructions):
        inst = instructions[cnt].split(" ")
        if inst[0][0] == "c":   # cpy
            if inst[1] in registers:
                registers[inst[2]] = registers[inst[1]]
            else:
                registers[inst[2]] = int(inst[1])
        elif inst[0][0] == "i": # inc
            registers[inst[1]] += 1
        elif inst[0][0] == "d": # dec
            registers[inst[1]] -= 1
        elif inst[0][0] == "j": # jnz
            if inst[2] in registers:
                jmp = registers[inst[2]]
            else:
                jmp = int(inst[2])
            if inst[1] in registers:
                if registers[inst[1]] != 0:
                    cnt += jmp
                    continue
            else:
                if int(inst[1]) != 0:
                    cnt += jmp
                    continue
        elif inst[0][0] == "o": # out
            transmission.append(registers[inst[1]])
            if len(transmission) == 16:
                return transmission == 8*[0, 1]
        else:                   # tgl
            jmp = cnt + registers[inst[1]]
            if jmp < len(instructions):
                tgl = instructions[jmp]
                inst = tgl.split()
                if len(inst) == 2:
                    if inst[0] == "inc":
                        instructions[jmp] = "dec " + inst[1]
                    else:
                        instructions[jmp] = "inc " + inst[1]
                else:
                    if inst[0] == "jnz":
                        instructions[jmp] = "cpy " + " ".join(inst[1:])
                    else:
                        instructions[jmp] = "jnz " + " ".join(inst[1:])
        # increment program counter
        cnt += 1

    return False

with open("input/25.txt", "r") as f:
    instructions = [x[:-1] for x in f] # drop "\n"
    for i in range(1000):
        if solve(instructions, {"a" : i, "b" : 0, "c" : 0, "d" : 0}):
            print(i)
            break