Advent_of_code/src/P8.py

from typing import List, Tuple

# --- Day 8: Handheld Halting ---

# Your flight to the major airline hub reaches cruising altitude without
# incident. While you consider checking the in-flight menu for one of those
# drinks that come with a little umbrella, you are interrupted by the kid
# sitting next to you.

# Their handheld game console won't turn on! They ask if you can take a look.

# You narrow the problem down to a strange infinite loop in the boot code
# (your puzzle input) of the device. You should be able to fix it, but first
# you need to be able to run the code in isolation.

# The boot code is represented as a text file with one instruction per line of
# text. Each instruction consists of an operation (acc, jmp, or nop) and an
# argument (a signed number like +4 or -20).

#     acc increases or decreases a single global value called the accumulator
# by the value given in the argument. For example, acc +7 would increase the
# accumulator by 7. The accumulator starts at 0. After an acc instruction, the
# instruction immediately below it is executed next.
#     jmp jumps to a new instruction relative to itself. The next instruction
# to execute is found using the argument as an offset from the jmp instruction;
# for example, jmp +2 would skip the next instruction, jmp +1 would continue to
# the instruction immediately below it, and jmp -20 would cause the instruction
# 20 lines above to be executed next.
#     nop stands for No OPeration - it does nothing. The instruction
# immediately below it is executed next.

# For example, consider the following program:

# nop +0
# acc +1
# jmp +4
# acc +3
# jmp -3
# acc -99
# acc +1
# jmp -4
# acc +6

# These instructions are visited in this order:

# nop +0  | 1
# acc +1  | 2, 8(!)
# jmp +4  | 3
# acc +3  | 6
# jmp -3  | 7
# acc -99 |
# acc +1  | 4
# jmp -4  | 5
# acc +6  |

# First, the nop +0 does nothing. Then, the accumulator is increased from 0 to
# 1 (acc +1) and jmp +4 sets the next instruction to the other acc +1 near the
# bottom. After it increases the accumulator from 1 to 2, jmp -4 executes,
# setting the next instruction to the only acc +3. It sets the accumulator to
# 5, and jmp -3 causes the program to continue back at the first acc +1.

# This is an infinite loop: with this sequence of jumps, the program will run
# forever. The moment the program tries to run any instruction a second time,
# you know it will never terminate.

# Immediately before the program would run an instruction a second time, the
# value in the accumulator is 5.

# Run your copy of the boot code. Immediately before any instruction is
# executed a second time, what value is in the accumulator?

with open("files/P8.txt", "r") as f:
    lines = [code for code in f.read().strip().split("\n")]


def part_1(lines: List[str], debug: bool = False) -> Tuple[int, bool]:
    accu = 0
    executed = []
    nline = 0
    while True:
        try:
            instr, acc = lines[nline].split(" ")
            if nline in executed:
                # we are in a for loop :(
                break
            else:
                executed.append(nline)
                if instr == "acc":
                    accu += int(acc)
                    nline += 1
                    continue
                elif instr == "jmp":
                    nline = nline + int(acc)
                    continue
                elif instr == "nop":
                    nline += 1
                    continue
        except IndexError:
            if debug:
                print("Code has run successfully")
            return accu, True
    if debug:
        print(f"The value of the accumulator was {accu} before exiting")
    return accu, False


# --- Part Two ---

# After some careful analysis, you believe that exactly one instruction is
# corrupted.

# Somewhere in the program, either a jmp is supposed to be a nop, or a nop is
# supposed to be a jmp. (No acc instructions were harmed in the corruption of
# this boot code.)

# The program is supposed to terminate by attempting to execute an instruction
# immediately after the last instruction in the file. By changing exactly one
# jmp or nop, you can repair the boot code and make it terminate correctly.

# For example, consider the same program from above:

# nop +0
# acc +1
# jmp +4
# acc +3
# jmp -3
# acc -99
# acc +1
# jmp -4
# acc +6

# If you change the first instruction from nop +0 to jmp +0, it would create a
# single-instruction infinite loop, never leaving that instruction. If you
# change almost any of the jmp instructions, the program will still eventually
# find another jmp instruction and loop forever.

# However, if you change the second-to-last instruction (from jmp -4 to
# nop -4), the program terminates! The instructions are visited in this order:

# nop +0  | 1
# acc +1  | 2
# jmp +4  | 3
# acc +3  |
# jmp -3  |
# acc -99 |
# acc +1  | 4
# nop -4  | 5
# acc +6  | 6

# After the last instruction (acc +6), the program terminates by attempting to
# run the instruction below the last instruction in the file. With this change,
# after the program terminates, the accumulator contains the value 8 (acc +1,
# acc +1, acc +6).

# Fix the program so that it terminates normally by changing exactly one jmp
# (to nop) or nop (to jmp). What is the value of the accumulator after the
# program terminates?


def part_2() -> None:
    for nline, _ in enumerate(lines):
        inst, acc = lines[nline].split(" ")
        # change instructions
        if inst == "nop":
            new_inst = "jmp"
        elif inst == "jmp":
            new_inst = "nop"

        # make a copy of the original code
        new_lines = lines.copy()
        # change line according to the instructions in the original code
        new_lines[nline] = " ".join((new_inst, acc))
        accu, has_ended = part_1(new_lines)
        if has_ended:
            print(f"The value of the accumulator was {accu} after terminates")
            break


if __name__ == "__main__":
    part_1(lines, debug=True)
    part_2()