advent-of-code/aoc2024/day04/main.go

package main

import (
	"bufio"
	_ "embed"
	"fmt"

	aoc "go.sour.is/advent-of-code"
)

// var log = aoc.Log

func main() { aoc.MustResult(aoc.Runner(run)) }

type result struct {
	valuePT1 int
	valuePT2 int
}

type record struct {
	p aoc.Point[int]
	d [2]int
}

func (r result) String() string { return fmt.Sprintf("%#v", r) }

func run(scan *bufio.Scanner) (*result, error) {

	m := make([][]rune, 0, 1000)
	var records []record
	var records2 []record

	for scan.Scan() {
		txt := scan.Text()
		m = append(m, []rune(txt))
	}

	for x, row := range m {
		for y, c := range row {
			if c == 'X' {
				rs := search1(record{
					p: aoc.Point[int]{x, y},
				}, m)
				records = append(records, rs...)
			}

			if c == 'A' {
				rs := search2(record{
					p: aoc.Point[int]{x, y},
				}, m)
				if len(rs) == 2 {
					records2 = append(records2, rs...)
				}
			}
		}
	}

	for _, r := range records2 {
		fmt.Println(r)
	}


	return &result{len(records), len(records2)/2}, nil
}

func search1(r record, m [][]rune) []record {
	var ds = [][2]int{
		{1, 0},   // up
		{0, 1},   // right
		{-1, 0},  // down
		{0, -1},  // left
		{1, 1},   // up-right
		{1, -1},  // up-left
		{-1, 1},  // down-right
		{-1, -1}, // down-left
	}

	var records []record

	for _, d := range ds {
		p := r.p
		if !check1(m, p, d) {
			continue
		}

		records = append(records, record{
			p: p,
			d: d,
		})
	}

	return records
}

func check1(m [][]rune, p aoc.Point[int], d [2]int) bool {
	for _, r := range []rune{'M', 'A', 'S'} {
		p[0] += d[0]
		p[1] += d[1]
		if p[0] < 0 || p[0] >= len(m) {
			return false
		}
		if p[1] < 0 || p[1] >= len(m[0]) {
			return false
		}
		if m[p[0]][p[1]] != r {
			return false
		}
	}

	return true
}

func search2(r record, m [][]rune) []record {
	var ds = [][2]int{
		{1, 1},   // up-right
		{1, -1},  // up-left
		{-1, 1},  // down-right
		{-1, -1}, // down-left
	}
	var records []record

	for _, d := range ds {
		p := r.p
		if !check2(m, p, d) {
			continue
		}

		records = append(records, record{
			p: p,
			d: d,
		})
	}

	return records
}

func check2(m [][]rune, p aoc.Point[int], d [2]int) bool {
	p0 := p[0] - d[0]
	p1 := p[1] - d[1]
	if p0 < 0 || p0 >= len(m) {
		return false
	}
	if p1 < 0 || p1 >= len(m[0]) {
		return false
	}
	if m[p0][p1] != 'M' {
		return false
	}

	p0 = p[0] + d[0]
	p1 = p[1] + d[1]
	if p0 < 0 || p0 >= len(m) {
		return false
	}
	if p1 < 0 || p1 >= len(m[0]) {
		return false
	}
	if m[p0][p1] != 'S' {
		return false
	}

	return true
}