aoc2024/day-08/internal/one/solve.go

package one

import (
	"bytes"
	"math"

	log "github.com/sirupsen/logrus"
)

func Solve(buf []byte) (int, error) {
	r := bytes.NewReader(buf)
	graph, err := parseLines(r)
	if err != nil {
		return 0, err
	}

	for i, a := range graph.antennae {
		for j, b := range graph.antennae {
			if i == j || a.identifier != b.identifier {
				continue
			}

			coords := calcAntiNodePos(a.coords, b.coords)
			if !graph.isOutOfBounds(coords) {
				_, ok := graph.antinodes[coords]
				if !ok {
					graph.antinodes[coords] = struct{}{}
				}
			}
		}
	}

	log.Debugf("\n%s\n", graph.debug())

	return len(graph.antinodes), nil
}

func calcAntiNodePos(a, b coords) coords {
	xdiff := int(math.Abs(float64(a.x - b.x)))
	ydiff := int(math.Abs(float64(a.y - b.y)))

	if a.x < b.x && a.y < b.y {
		return newCoords(b.x+xdiff, b.y+ydiff)
	} else if a.x < b.x && a.y > b.y {
		return newCoords(b.x+xdiff, b.y-ydiff)
	} else if a.x > b.x && a.y < b.y {
		return newCoords(b.x-xdiff, b.y+ydiff)
	} else {
		return newCoords(b.x-xdiff, b.y-ydiff)
	}
}