13
π - 2025 DAY 10 SOLUTIONS - π
(programming.dev)
Go
Linear programming all over again! I solved part 1 with a BFS like many. But for part 2 a proper solver was needed. I'm terrible at LP so I tried to use a simplex implementation, but it was not enough to find a solution, Z3 was needed but I couldn't bother to install anything so... screw it.
Here is my proposal part 2 doesn't work but the modelisation is interesting enough that it is worth posting:
day10.go
package main
import (
"aoc/utils"
"fmt"
"math"
"regexp"
"slices"
"strconv"
"strings"
"sync"
"gonum.org/v1/gonum/mat"
"gonum.org/v1/gonum/optimize/convex/lp"
)
type button []int8
type problem struct {
want int
buttons []button
joltageRequirements []int8
}
func parseLights(lights string) (want int) {
want = 0
for idx, ch := range lights {
if ch == '#' {
want += (1 << idx)
}
}
return want
}
func parseProblem(line string) problem {
reg := regexp.MustCompile(`\[([.#]+)\] ((?:(?:\([^)]+\))\s*)+) {([^}]+)}`)
matches := reg.FindStringSubmatch(line)
lights := matches[1]
buttonString := matches[2]
joltage := matches[3]
buttonString = string(slices.DeleteFunc(
[]rune(buttonString),
func(ch rune) bool {
return ch == '(' || ch == ')'
}))
buttons := []button{}
for switchString := range strings.SplitSeq(buttonString, " ") {
switches := []int8{}
for sw := range strings.SplitSeq(switchString, ",") {
val, _ := strconv.Atoi(sw)
switches = append(switches, int8(val))
}
buttons = append(buttons, switches)
}
joltageRequirements := []int8{}
for req := range strings.SplitSeq(joltage, ",") {
val, _ := strconv.Atoi(req)
joltageRequirements = append(joltageRequirements, int8(val))
}
return problem{
want: parseLights(lights),
buttons: buttons,
joltageRequirements: joltageRequirements,
}
}
func getProblemChannel(input chan string) chan problem {
ch := make(chan problem, cap(input))
go func() {
for line := range input {
ch <- parseProblem(line)
}
close(ch)
}()
return ch
}
func (b button) value() (val int) {
val = 0
for _, sw := range b {
val += 1 << sw
}
return val
}
func bfs(goal int, buttons []button) int {
type bfsState struct {
epoch int8
value int
}
visited := []int{0}
queue := []bfsState{}
for _, bt := range buttons {
value := bt.value()
queue = append(queue, bfsState{epoch: 1, value: value})
visited = append(visited, value)
}
for len(queue) > 0 {
state := queue[0]
queue = queue[1:]
if state.value == goal {
return int(state.epoch)
}
for _, bt := range buttons {
nextValue := state.value ^ bt.value()
if !slices.Contains(visited, nextValue) {
visited = append(visited, nextValue)
queue = append(queue, bfsState{
epoch: state.epoch + 1,
value: nextValue,
})
}
}
}
return math.MaxInt
}
func (p problem) solve() int {
depth := bfs(p.want, p.buttons)
return int(depth)
}
func parallel(threadCount int, f func(thrId int)) {
var wg sync.WaitGroup
for id := range threadCount {
wg.Go(func() {
f(id)
})
}
wg.Wait()
}
func stepOne(input chan string) (int, error) {
sum := 0
pbChan := getProblemChannel(input)
for pb := range pbChan {
depth := pb.solve()
fmt.Println(depth)
sum += depth
}
return sum, nil
}
type linearEquation struct {
solution int
coeffs []int
}
func (p problem) toLinearEquations() linearProblem {
equations := make([]linearEquation, len(p.joltageRequirements))
varCount := len(p.buttons)
for equIdx, solution := range p.joltageRequirements {
equ := linearEquation{
solution: int(solution),
coeffs: make([]int, varCount),
}
for btIdx, bt := range p.buttons {
if slices.Contains(bt, int8(equIdx)) {
equ.coeffs[btIdx] = 1
}
}
equations[equIdx] = equ
}
return equations
}
type linearProblem []linearEquation
func (lp linearProblem) A() mat.Matrix {
rows := len(lp)
cols := len(lp[0].coeffs)
data := make([]float64, rows*cols)
for r := range rows {
for c := range cols {
data[r*cols+c] = float64(lp[r].coeffs[c])
}
fmt.Println(data[r*cols : (r+1)*cols])
}
return mat.NewDense(rows, cols, data)
}
func (lp linearProblem) c() []float64 {
count := len(lp[0].coeffs)
consts := make([]float64, count)
for idx := range count {
consts[idx] = 1.0
}
return consts
}
func (lp linearProblem) b() []float64 {
bees := make([]float64, len(lp))
for idx := range bees {
bees[idx] = float64(lp[idx].solution)
}
return bees
}
func stepTwo(input chan string) (int, error) {
sum := 0
pbChan := getProblemChannel(input)
for pb := range pbChan {
lpb := pb.toLinearEquations()
c := lpb.c()
A := lpb.A()
b := lpb.b()
optF, _, err := lp.Simplex(c, A, b, 1.0, nil)
if err != nil {
fmt.Errorf("simplex error: %v\n", err)
}
fmt.Println(optF)
sum += int(optF)
}
return sum, nil
}
func main() {
input := utils.FilePath("day10.txt")
utils.RunStep(utils.ONE, input, stepOne)
utils.RunStep(utils.TWO, input, stepTwo)
}