adventofcode/2024/02/main.go

package main

import (
	"fmt"
	"sort"

	"aoc/helper"
)

type reports []report
type report struct {
	levels []int
}

func main() {
	// generate reports
	var reports reports
	for _, val := range helper.ReadLinesToIntSlices() {
		reports = append(reports, report{levels: val})
	}

	// part 1
	save_count := 0
	for _, r := range reports {
		if r.isSave() {
			save_count++
		}
	}
	fmt.Printf("Save reports: %d\n", save_count)

	// part 2
	save_count = 0
	for _, r := range reports {
		if r.isSaveWithDamper() {
			save_count++
		}
	}
	fmt.Printf("Save reports (with damper): %d\n", save_count)
}

func (r report) isSave() bool {
	if !r.isSorted() {
		return false
	}

	for i := range len(r.levels) - 1 { // iterate til second last level
		if !isValidLevelDifference(r.levels[i], r.levels[i+1]) {
			return false
		}
	}

	return true
}

func (r report) isSorted() bool {
	ascSorted := sort.SliceIsSorted(
		r.levels,
		func(i, j int) bool { return r.levels[i] < r.levels[j] },
	)
	descSorted := sort.SliceIsSorted(
		r.levels,
		func(i, j int) bool { return r.levels[i] > r.levels[j] },
	)

	return ascSorted || descSorted
}

func isValidLevelDifference(i int, j int) bool {
	if i == j {
		return false
	}

	if helper.Abs(i-j) > 3 {
		return false
	}

	return true
}

func (r report) isSaveWithDamper() bool {
	if r.isSave() {
		return true
	}

	for i := range r.levels {
		// remove one item from report and try to validate
		if r.removeLevelByIndex(i).isSave() {
			return true
		}
	}

	return false
}

func (r report) removeLevelByIndex(dropIndex int) report {
	var newlevels []int
	// create new slice w/o passed index position
	newlevels = append(newlevels, r.levels[:dropIndex]...)
	newlevels = append(newlevels, r.levels[dropIndex+1:]...)

	return report{levels: newlevels}
}