aoc-2025/aoc_day1.py at main · vortydev/aoc-2025 · GitHub

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# aoc_day1.py
# https://adventofcode.com/2025/day/1
from colorama import Fore, Style, init
init(autoreset=True)

C_INPUT = Fore.CYAN
C_POS   = Fore.GREEN
C_X     = Fore.YELLOW
C_GREY  = Fore.LIGHTBLACK_EX
C_BLACK = Fore.BLACK
C_CYAN  = Fore.LIGHTCYAN_EX
C_BLUE  = Fore.LIGHTBLUE_EX
C_MAGENTA = Fore.LIGHTMAGENTA_EX
C_HEAD  = Fore.MAGENTA
C_RST   = Style.RESET_ALL


START_POS = 50
MIN_POS = 0
MAX_POS = 99
DIAL_SIZE = MAX_POS - MIN_POS + 1  # 100

def day1():
    instructions: list[tuple[str, int]] = []

    with open("day1_input.txt", "r", encoding="utf-8") as f:
        for line in f:
            line = line.strip()
            if not line:
                continue
            direction = line[0]          # "L" or "R"
            value = int(line[1:])        # rest of the string
            instructions.append((direction, value))

    print(f"Instructions ({len(instructions)}) loaded.")

    day1_task1(instructions)
    day1_task2(instructions)

def day1_task1(instructions: list[tuple[str, int]] = []):
    print("\n##### Day 1 - Task 1 #####")

    zero_counter = 0
    cur_pos = START_POS
    # print(f"Starting pos:", cur_pos)

    for direction, val in instructions:
        # print("Input:", direction, val)

        if direction == "L":
            # move left (backwards)
            cur_pos = ((cur_pos - val - MIN_POS) % DIAL_SIZE) + MIN_POS
        elif direction == "R":
            # move right (forwards)
            cur_pos = ((cur_pos + val - MIN_POS) % DIAL_SIZE) + MIN_POS
        else:
            raise ValueError(f"Unexpected direction {direction!r}")

        # print("Now at:", cur_pos)
        if cur_pos == 0:
            zero_counter += 1

    print("Times on 0:", zero_counter)


def step_and_count(cur_pos: int, direction: str, val: int) -> tuple[int, int]:
    # +val for R, -val for L
    delta = val if direction == "R" else -val

    # how many times we cross/hit 0 during this move
    if delta > 0:
        # moving right: positions p+1 .. p+delta
        crosses = (cur_pos + delta) // DIAL_SIZE
    elif delta < 0:
        # moving left: mirror the dial and reuse the "right" logic
        d = -delta
        mirror_pos = (DIAL_SIZE - cur_pos) % DIAL_SIZE
        crosses = (mirror_pos + d) // DIAL_SIZE
    else:
        crosses = 0

    # new wrapped position
    new_pos = (cur_pos + delta) % DIAL_SIZE
    return crosses, new_pos

def day1_task2(instructions: list[tuple[str, int]]):
    print("\n##### Day 1 - Task 2 #####")
    zero_counter = 0
    cur_pos = START_POS

    for direction, val in instructions:
        crosses, cur_pos = step_and_count(cur_pos, direction, val)
        zero_counter += crosses

        # debug if you want:
        color = (
            C_GREY     if crosses == 0 else
            C_CYAN     if crosses == 1 else
            C_MAGENTA
        )
        print(f"{C_BLACK}Input:{C_RST} {direction} {val}")
        print(f"{C_POS}Current val {cur_pos}{C_RST} {C_X}(+0 {color}x{crosses}){C_RST}")

    print(f"{C_HEAD}Times passing 0: {zero_counter}{C_RST}")


if __name__ == "__main__":
    try:
        day1()
    except Exception as e:
        print(f"Fatal error: {e}")
        exit(-1)