advent-of-code-2024/go/question8/main.go

package main

import (
	"fmt"
	"math/big"
	"strings"
)

type Map struct {
	data   []rune
	width  int
	height int
}
type Point struct {
	x, y int
}

func (p *Point) String() string {
	return fmt.Sprintf("(%d, %d)", p.x, p.y)
}

func (p *Point) IsBetween(p1 *Point, p2 *Point) bool {
	return isBetween(p.x, p1.x, p2.x) && isBetween(p.y, p1.y, p2.y)

}

// Returns true is a is between (x, y) disregarding
// x, y order ( (x,y) is considered an interval.
// The definition of between includes both ends
func isBetween(a int, x int, y int) bool {
	if x > y {
		return isBetween(a, y, x)
	}
	return x <= a && a <= y

}

func (p *Point) Dist(p2 *Point) *Vector {
	return NewVecFromInt(p2.x-p.x, p2.y-p.y)
}

func NewVecFromInt(x, y int) *Vector {
	return &Vector{big.NewRat(int64(x), 1), big.NewRat(int64(y), 1)}
}

type Vector struct {
	x, y *big.Rat
}

func (v *Vector) String() string {
	return fmt.Sprintf("(%s, %s)", v.x, v.y)
}

func (v *Vector) Time(n *big.Rat) *Vector {
	return &Vector{new(big.Rat).Mul(v.x, n), new(big.Rat).Mul(v.y, n)}
}

func (v *Vector) Opp() *Vector {
	return v.Time(big.NewRat(-1, 1))
}

func (v *Vector) Plus(vec2 *Vector) *Vector {
	return &Vector{new(big.Rat).Add(v.x, vec2.x), new(big.Rat).Add(v.y, vec2.y)}
}

func (v *Vector) AsPoint() *Point {
	if !v.x.IsInt() || !v.y.IsInt() {
		panic("Not a point")
	}
	return &Point{int(v.x.Num().Int64()), int(v.y.Num().Int64())}
}

func BaryCenter(p1, p2 *Point) *Vector {
	return &Vector{
		big.NewRat(int64(p1.x+p2.x), 2),
		big.NewRat(int64(p1.y+p2.y), 2),
	}
}

func (m *Map) isInbound(point *Point) bool {
	return point.x >= 0 && point.x < m.width && point.y >= 0 && point.y < m.width
}

func (m *Map) Get(point *Point) (rune, bool) {
	if !m.isInbound(point) {
		return 0, false
	}
	idx := point.x + m.width*point.y
	return m.data[idx], true
}

func (m *Map) getByDataIndex(idx int) *Point {
	x := idx % m.width
	y := idx / m.width
	return &Point{x, y}
}

func NewMap(input string) *Map {
	if !strings.HasSuffix(input, "\n") {
		input += "\n"
	}
	width := strings.Index(input, "\n")
	height := strings.Count(input, "\n")
	data := []rune(strings.ReplaceAll(input, "\n", ""))
	return &Map{data, width, height}
}

func (m *Map) getAllAntennaFrequencies() <-chan rune {
	ch := make(chan rune)
	go func() {
		dejaVu := make(map[rune]bool)
		dejaVu['.'] = true
		for _, r := range m.data {
			if _, ok := dejaVu[r]; !ok {
				dejaVu[r] = true
				ch <- r
			}
		}
		close(ch)
	}()
	return ch
}

func (m *Map) getAllAntennaOfFrequency(freq rune) []*Point {
	ret := make([]*Point, 0)
	for i, r := range m.data {
		if r == freq {
			ret = append(ret, m.getByDataIndex(i))
		}
	}
	return ret
}

type AntennaPair struct {
	antenna1 *Point
	antenna2 *Point
	freq     rune
}

func (m *Map) getAllAntennaPairsOfFrequency(freq rune) <-chan *AntennaPair {
	antennas := m.getAllAntennaOfFrequency(freq)
	ch := make(chan *AntennaPair)
	go func() {
		for i := 0; i < len(antennas); i++ {
			for j := i + 1; j < len(antennas); j++ {
				ch <- &AntennaPair{antennas[i], antennas[j], freq}
			}
		}
		close(ch)

	}()
	return ch
}

func (m *Map) getEquidistantAntinodeLocationsForFreq(freq rune) <-chan *Point {
	ch := make(chan *Point)
	go func() {
		for p := range m.getAllAntennaPairsOfFrequency(freq) {
			bc := BaryCenter(p.antenna1, p.antenna2)
			dist := p.antenna1.Dist(p.antenna2).Time(big.NewRat(3, 2))
			antiNode1 := bc.Plus(dist).AsPoint()
			antiNode2 := bc.Plus(dist.Opp()).AsPoint()
			if m.isInbound(antiNode1) {
				ch <- antiNode1
			}
			if m.isInbound(antiNode2) {
				ch <- antiNode2
			}
		}
		close(ch)
	}()

	return ch
}

func (m *Map) generateInlinePoints(p *Point, stepX, stepY int, filter func(*Point) bool, ch chan<- *Point) {
	for {
		p = &Point{p.x + stepX, p.y + stepY}
		if !m.isInbound(p) {
			return
		}
		if filter(p) {
			ch <- p
		}

	}
}

func (m *Map) getStep(p *AntennaPair) (int, int) {
	dist := p.antenna1.Dist(p.antenna2)
	if dist.x.Cmp(big.NewRat(0, 1)) == 0 {
		return 0, 1
	}
	if dist.y.Cmp(big.NewRat(0, 1)) == 0 {
		return 1, 0
	}
	step := new(big.Rat).Quo(dist.y, dist.x)
	stepX := int(step.Denom().Int64())
	stepY := int(step.Num().Int64())
	if stepX < 0 {
		stepX = -stepX
	}
	return stepX, stepY
}

func (m *Map) getCollinearAntinodeLocationsFreq(freq rune) <-chan *Point {
	ch := make(chan *Point)
	go func() {
		for pair := range m.getAllAntennaPairsOfFrequency(freq) {
			stepX, stepY := m.getStep(pair)
			filter := func(p *Point) bool {
				return !p.IsBetween(pair.antenna1, pair.antenna2)
			}
			m.generateInlinePoints(pair.antenna1, stepX, stepY, filter, ch)
			m.generateInlinePoints(pair.antenna1, -stepX, -stepY, filter, ch)

		}
		close(ch)
	}()

	return ch
}

func dedupPoints(points <-chan *Point) <-chan *Point {
	ch := make(chan *Point)
	go func() {
		m := make(map[int]map[int]bool)
		for p := range points {
			if _, ok := m[p.x]; ok {
				if _, ok2 := m[p.x][p.y]; ok2 {
					continue
				}
				m[p.x][p.y] = true
			} else {
				m[p.x] = make(map[int]bool)
				m[p.x][p.y] = true
			}
			ch <- p
		}
		close(ch)
	}()

	return ch

}

func (m *Map) getAllEquidistantAntinodeLocations() <-chan *Point {
	ch := make(chan *Point)
	go func() {
		for freq := range m.getAllAntennaFrequencies() {
			for p := range m.getEquidistantAntinodeLocationsForFreq(freq) {
				ch <- p
			}
		}
		close(ch)
	}()
	return dedupPoints(ch)
}

func (m *Map) getAllCollinearAntinodeLocations() <-chan *Point {
	ch := make(chan *Point)
	go func() {
		for freq := range m.getAllAntennaFrequencies() {
			for p := range m.getCollinearAntinodeLocationsFreq(freq) {
				ch <- p
			}
		}
		close(ch)
	}()
	return dedupPoints(ch)
}

func question8A(input string) int {
	i := 0
	m := NewMap(input)
	for _ = range m.getAllEquidistantAntinodeLocations() {
		i++
	}
	return i

}

func question8B(input string) int {
	i := 0
	m := NewMap(input)
	for _ = range m.getAllCollinearAntinodeLocations() {
		//fmt.Println(">> ", p)
		i++
	}
	return i

}

func main() {

	fmt.Printf("The answer to question 8A is %d \n", question8A(realInput))
	fmt.Printf("The answer to question 8B is %d \n", question8B(mockInput))

}