advent_of_code_2025/1/solve_2.go

package main

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

func main() {
	fmt.Println("Advent of Code 2025 - Day 1 - Part 2")
	nb_occ_zero, lock_num := 0, 50
	var direction, nb_ticks, prev_lock_num, nb_cycles int
	var instruction string

	f, _ := os.Open("1/input")
	defer f.Close()

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		instruction = scanner.Text()
		switch instruction[0] {
		case 'L':
			direction = -1
		case 'R':
			direction = 1
		default:
			panic("unrecognized instruction")
		}

		nb_ticks, _ = strconv.Atoi(instruction[1:])
		prev_lock_num = lock_num

		lock_num, nb_cycles = (lock_num+direction*nb_ticks)%100, (direction*nb_ticks)/100
		if lock_num < 0 {
			lock_num += 100
		}
		
		nb_occ_zero += int(math.Abs(float64(nb_cycles)))

		if prev_lock_num == 0 {
			continue
		}

		if lock_num == 0 {
			nb_occ_zero++
		} else if direction == -1 && lock_num > prev_lock_num {
			nb_occ_zero++
		} else if direction == 1 && lock_num < prev_lock_num {
			nb_occ_zero++
		}

	}

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

	fmt.Println(nb_occ_zero)
}