advent_of_code_2025/1/solve_1.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
)

func main() {
	fmt.Println("Advent of Code 2025 - Day 1 - Part 1")
	nb_occ_zero := 0
	lock_num := 50
	direction := 1
	var nb_ticks int
	var instruction string
	f, err := os.Open("1/input")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	scanner := bufio.NewScanner(f)

	// We read input line by line
	for scanner.Scan() {
		instruction = scanner.Text()
		switch instruction[0] {
		case 'L':
			direction = -1
		case 'R':
			direction = 1
		default:
			panic("unrecognized instruction")
		}
		nb_ticks, err = strconv.Atoi(instruction[1:])
		if err != nil {
			log.Fatal(err)
		}
		lock_num = (lock_num + direction*nb_ticks) % 100
		if lock_num < 0 {
			lock_num = lock_num + 100
		}
		if lock_num == 0 {
			nb_occ_zero++
		}
	}

	if err = scanner.Err(); err != nil {
		log.Fatal(err)
	}

	fmt.Println(nb_occ_zero)
}