adventoc/2024/day04.go

package adventoc2024

import (
	"bufio"
	"io"
)

type Day4 struct{}

func (d Day4) Part1(r io.Reader) string {
	wordsearch := make([][]rune, 0)
	s := bufio.NewScanner(r)
	var sum int

	for s.Scan() {
		line := []rune(s.Text())
		wordsearch = append(wordsearch, line)
	}

	search := make([]rune, 4)
	for startx := range wordsearch {
		for starty := range wordsearch[startx] {
			for dx := -1; dx < 2; dx++ {
				for dy := -1; dy < 2; dy++ {
					for i := 0; i < 4; i++ {
						x := startx + dx*i
						y := starty + dy*i
						search[i] = runeAt(wordsearch, x, y)
					}
					if string(search) == "XMAS" {
						sum++
					}
				}
			}

		}
	}

	return printi(sum)
}

func (d Day4) Part2(r io.Reader) string {
	wordsearch := make([][]rune, 0)
	s := bufio.NewScanner(r)
	var sum int

	for s.Scan() {
		line := []rune(s.Text())
		wordsearch = append(wordsearch, line)
	}

	s1 := make([]rune, 3)
	s2 := make([]rune, 3)
	for startx := range wordsearch {
		for starty := range wordsearch[startx] {

			toptobottom := [][]int{
				{-1, -1},
				{0, 0},
				{1, 1},
			}

			for i, transpose := range toptobottom {
				x, y := startx+transpose[0], starty+transpose[1]
				s1[i] = runeAt(wordsearch, x, y)
			}

			bottomtotop := [][]int{
				{-1, 1},
				{0, 0},
				{1, -1},
			}

			for i, transpose := range bottomtotop {
				x, y := startx+transpose[0], starty+transpose[1]
				s2[i] = runeAt(wordsearch, x, y)

			}

			if str1, str2 := string(s1), string(s2); (str1 == "SAM" || str1 == "MAS") && (str2 == "SAM" || str2 == "MAS") {
				sum++
			}

		}
	}

	return printi(sum)
}

func runeAt(r [][]rune, x, y int) rune {
	if x >= len(r) || x < 0 {
		return rune(0)
	}

	if y >= len(r[x]) || y < 0 {
		return rune(0)
	}

	return r[x][y]
}