adventofcode/2025/day10/main.go

package main

import (
	"fmt"
	"slices"
	"strings"
	"sync"

	"github.com/draffensperger/golp"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToStringSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []string) {
	machines := parseInput(inp)
	var ret int
	for _, m := range machines {
		r := m.Start()
		ret += r
	}

	fmt.Println("# Part 1")
	fmt.Println(ret)
}

func part2(inp []string) {
	machines := parseInput(inp)
	var ret int
	var wg sync.WaitGroup
	for _, m := range machines {
		wg.Go(func() {
			sol := m.SolveJoltage()
			ret += sol
		})
	}
	wg.Wait()
	fmt.Println("# Part 2")
	fmt.Println(ret)
}

func parseInput(inp []string) []*Machine {
	var ret []*Machine
	for i := range inp {
		ret = append(ret, NewMachine(i, inp[i]))
	}
	return ret
}

type Machine struct {
	id        int
	numLights int
	lights    int
	wLights   int
	buttons   [][]int
	joltages  []int
	jCounters []int
}

func NewMachine(id int, inp string) *Machine {
	ret := Machine{id: id}
	pts := strings.Fields(inp)
	for _, p := range pts {
		in := p[1 : len(p)-1]
		switch p[0] {
		case '[':
			var l []int
			for i := range in {
				if in[i] == '#' {
					l = append(l, i)
				}
			}
			ret.wLights = intsToBitmask(l)
			ret.numLights = len(in)
		case '(':
			wP := strings.Split(in, ",")
			var w []int
			for i := range wP {
				w = append(w, h.Atoi(wP[i]))
			}
			ret.buttons = append(ret.buttons, w)
		case '{':
			wJ := strings.Split(in, ",")
			for i := range wJ {
				ret.joltages = append(ret.joltages, h.Atoi(wJ[i]))
				ret.jCounters = append(ret.jCounters, 0)
			}
		}
	}
	return &ret
}

// Start presses buttons until the machine is running
func (m *Machine) Start() int {
	bMasks := []int{}
	for _, b := range m.buttons {
		bMasks = append(bMasks, intsToBitmask(b))
	}
	// Start at the end
	endMask := 0
	current := map[int]bool{m.wLights: true}
	var ret int
	for p := 1; p <= 1000; p++ {
		nextSet := make(map[int]bool)
		for c := range current {
			for _, b := range bMasks {
				nextSet[c^b] = true
			}
		}
		current = nextSet
		if _, exists := current[endMask]; exists {
			return p
		}
	}
	return ret
}

func (m *Machine) SolveJoltage() int {
	if slices.Equal(m.jCounters, m.joltages) {
		return 0
	}

	nB := len(m.buttons)
	nJ := len(m.joltages)

	lp := golp.NewLP(0, nB)
	lp.SetVerboseLevel(golp.NEUTRAL)

	objCoeffs := make([]float64, nB)
	for i := range nB {
		objCoeffs[i] = 1.0
	}
	lp.SetObjFn(objCoeffs)

	for i := range nB {
		lp.SetInt(i, true)
		lp.SetBounds(i, 0.0, float64(1000))
	}
	for i := 0; i < nJ; i++ {
		var entries []golp.Entry
		for j, btn := range m.buttons {
			if slices.Contains(btn, i) {
				entries = append(entries, golp.Entry{Col: j, Val: 1.0})
			}
		}
		targetValue := float64(m.joltages[i])
		if err := lp.AddConstraintSparse(entries, golp.EQ, targetValue); err != nil {
			panic(err)
		}
	}

	status := lp.Solve()
	if status != golp.OPTIMAL {
		return 0
	}

	solution := lp.Variables()
	totalPresses := 0
	for _, val := range solution {
		totalPresses += int(val + 0.5)
	}
	return totalPresses
}

func (m *Machine) Reset() { m.lights = 0 }

func (m Machine) String() string {
	l := bitmaskToBytes(m.lights, m.numLights)
	wl := bitmaskToBytes(m.wLights, m.numLights)
	return fmt.Sprintf("[%s] -> [%s] %d", string(l), string(wl), m.wLights)
}

func intsToBitmask(i []int) int {
	mask := 0
	for _, v := range i {
		mask |= 1 << v
	}
	return mask
}
func bitmaskToInts(in int, length int) []int {
	var ret []int
	for i := 0; i < length; i++ {
		if in&1 == 1 {
			ret = append(ret, i)
		}
		in = in >> 1
	}
	return ret
}

func bitmaskToBytes(in int, length int) []byte {
	var ret []byte
	for i := 1; i <= length; i++ {
		if in&1 == 1 {
			ret = append(ret, '#')
		} else {
			ret = append(ret, '.')
		}
		in = in >> 1
	}
	return ret
}

func elim(mtx [][]int) ([]int, [][]int) {
	m := len(mtx)
	if m == 0 {
		return nil, nil
	}
	n := len(mtx[0]) - 1
	pivCols := []int{}
	cRow := 0
	mat := make([][]int, m)
	for i := range mtx {
		mat[i] = make([]int, n+1)
		copy(mat[i], mtx[i])
	}
	for col := 0; col < n && cRow < m; col++ {
		pivRow := -1
		for row := cRow; row < m; row++ {
			if mat[row][col] != 0 {
				pivRow = row
				break
			}
		}
		if pivRow == -1 {
			continue
		}

		mat[cRow], mat[pivRow] = mat[pivRow], mat[cRow]
		pivCols = append(pivCols, col)

		for row := cRow + 1; row < m; row++ {
			if mat[row][col] != 0 {
				factor := mat[row][col]
				pivVal := mat[cRow][col]
				for j := col; j <= n; j++ {
					mat[row][j] = mat[row][j]*pivVal - mat[cRow][j]*factor
				}
			}
		}
		cRow++
	}
	return pivCols, mat
}