main.go

package main

import (
	"fmt"
	"io"
	"strings"

	lib "github.com/teivah/advent-of-code"
)

func fs1(reader io.Reader) int {
	s := lib.ReaderToString(reader)
	codes := lib.StringsToInts(strings.Split(s, ","))

	const (
		maxRow = 50
		maxCol = 50
	)

	sum := 0
	for row := 0; row < maxRow; row++ {
		for col := 0; col < maxCol; col++ {
			state := run(codes, func(state *State) {
				state.buffer = []int{col, row}
			})
			sum += state.sum
		}
	}

	return sum
}

func run(codes []int, postActions func(*State)) *State {
	state := &State{
		memory: append(codes, make([]int, 10000)...),
		offset: 0,
		over:   false,
		//debug:  true,

		col: -1,
		row: 0,
	}
	state.functions = map[int]Apply{
		1:  state.plus,
		2:  state.mult,
		3:  state.in,
		4:  state.out,
		5:  state.jnz,
		6:  state.jiz,
		7:  state.lt,
		8:  state.eq,
		9:  state.rlt,
		99: state.exit,
	}

	if postActions != nil {
		postActions(state)
	}

	for !state.over {
		if state.offset >= len(codes) {
			break
		}
		state.execute()
	}

	return state
}

func (s *State) execute() {
	opcode := toOpcode(s.memory[s.offset])
	s.functions[opcode.opcode](opcode.ctx)
}

type Opcode struct {
	opcode int
	ctx    Context
}

func toOpcode(i int) Opcode {
	var v []int
	for i != 0 {
		v = append(v, i%10)
		i /= 10
	}

	res := make([]int, 0, len(v))
	for idx := 0; idx < 5-len(v); idx++ {
		res = append(res, 0)
	}

	for idx := 0; idx < len(v); idx++ {
		res = append(res, v[len(v)-idx-1])
	}

	return Opcode{
		opcode: res[3]*10 + res[4],
		ctx: Context{
			modes: []int{res[2], res[1], res[0]},
		},
	}
}

type State struct {
	debug        bool
	memory       []int
	offset       int
	over         bool
	functions    map[int]Apply
	relativeBase int

	sum    int
	row    int
	col    int
	buffer []int
}

type UnitType int

const (
	scaffold UnitType = iota
	empty
)

type Context struct {
	modes []int
}

func (c Context) String() string {
	var s []string
	for _, mode := range c.modes {
		switch mode {
		case 0:
			s = append(s, "position")
		case 1:
			s = append(s, "immediate")
		case 2:
			s = append(s, "relative")
		default:
			panic(mode)
		}
	}
	return fmt.Sprintf("[%s]", strings.Join(s, ", "))
}

func (c Context) Until(i int) string {
	var s []string
	for _, mode := range c.modes[:i] {
		switch mode {
		case 0:
			s = append(s, "position")
		case 1:
			s = append(s, "immediate")
		case 2:
			s = append(s, "relative")
		default:
			panic(mode)
		}
	}
	return fmt.Sprintf("[%s]", strings.Join(s, ", "))
}

type Apply func(ctx Context)

func (s *State) get(ctx Context, parameter int) int {
	instructionIndex := s.offset + 1 + parameter
	instructionValue := s.memory[instructionIndex]

	switch ctx.modes[parameter] {
	case 0: // Position
		return s.memory[instructionValue]
	case 1: // Immediate
		return instructionValue
	case 2: // Relative
		return s.memory[instructionValue+s.relativeBase]
	default:
		panic(ctx.modes[parameter])
	}
}

func (s *State) set(ctx Context, parameter, value int) {
	s.memory[s.index(ctx, parameter)] = value
}

func (s *State) index(ctx Context, parameter int) int {
	instructionIndex := s.offset + 1 + parameter
	instructionValue := s.memory[instructionIndex]

	switch ctx.modes[parameter] {
	case 0: // Position
		return instructionValue
	case 1: // Immediate
		panic(ctx.modes[parameter])
	case 2: // Relative
		return instructionValue + s.relativeBase
	default:
		panic(ctx.modes[parameter])
	}
}

func (s *State) plus(ctx Context) {
	if s.debug {
		fmt.Println("plus", ctx, s.memory[s.offset+1], s.memory[s.offset+2], s.memory[s.offset+3])
	}

	s.set(ctx, 2, s.get(ctx, 0)+s.get(ctx, 1))
	s.offset += 4
}

func (s *State) mult(ctx Context) {
	if s.debug {
		fmt.Println("mult", ctx, s.memory[s.offset+1], s.memory[s.offset+2], s.memory[s.offset+3])
	}

	s.set(ctx, 2, s.get(ctx, 0)*s.get(ctx, 1))
	s.offset += 4
}

func (s *State) in(ctx Context) {
	if s.debug {
		fmt.Println("in", ctx.Until(1), s.memory[s.offset+1])
	}

	if len(s.buffer) != 0 {
		s.set(ctx, 0, s.buffer[0])
		s.buffer = s.buffer[1:]
	}
	s.offset += 2
}

func (s *State) out(ctx Context) {
	if s.debug {
		fmt.Println("out", ctx.Until(1), s.memory[s.offset+1])
	}

	v := s.get(ctx, 0)

	if v == 1 {
		s.sum++
	}

	s.offset += 2
}

func (s *State) jnz(ctx Context) {
	if s.debug {
		fmt.Println("jnz", ctx.Until(2), s.memory[s.offset+1], s.memory[s.offset+2])
	}

	if s.get(ctx, 0) != 0 {
		s.offset = s.get(ctx, 1)
	} else {
		s.offset += 3
	}
}

func (s *State) jiz(ctx Context) {
	if s.debug {
		fmt.Println("jiz", ctx.Until(2), s.memory[s.offset+1], s.memory[s.offset+2])
	}

	if s.get(ctx, 0) == 0 {
		s.offset = s.get(ctx, 1)
	} else {
		s.offset += 3
	}
}

func (s *State) lt(ctx Context) {
	if s.debug {
		fmt.Println("lt", ctx, s.memory[s.offset+1], s.memory[s.offset+2], s.memory[s.offset+3])
	}

	if s.get(ctx, 0) < s.get(ctx, 1) {
		s.set(ctx, 2, 1)
	} else {
		s.set(ctx, 2, 0)
	}
	s.offset += 4
}

func (s *State) eq(ctx Context) {
	if s.debug {
		fmt.Println("eq", ctx, s.memory[s.offset+1], s.memory[s.offset+2], s.memory[s.offset+3])
	}

	if s.get(ctx, 0) == s.get(ctx, 1) {
		s.set(ctx, 2, 1)
	} else {
		s.set(ctx, 2, 0)
	}
	s.offset += 4
}

func (s *State) rlt(ctx Context) {
	if s.debug {
		fmt.Println("rlt", ctx.Until(1), s.memory[s.offset+1])
	}

	s.relativeBase += s.get(ctx, 0)
	s.offset += 2
}

func (s *State) exit(ctx Context) {
	s.over = true
}

func fs2(reader io.Reader) int {
	s := lib.ReaderToString(reader)
	codes := lib.StringsToInts(strings.Split(s, ","))

	const (
		squareRow = 100
		squareCol = 100
	)

	grid := make(map[lib.Position]bool)

	maxRow := 100
	maxCol := 100
	for {
		for row := 0; row < maxRow; row++ {
			for col := 0; col < maxCol; col++ {
				pos := lib.Position{row, col}
				if _, exists := grid[pos]; exists {
					continue
				}

				state := run(codes, func(state *State) {
					state.buffer = []int{col, row}
				})
				if state.sum == 1 {
					grid[pos] = true
				} else {
					grid[pos] = false
				}
			}
		}

	root:
		for row := 0; ; row++ {
			if row >= maxRow {
				break
			}

			col := 0
			for ; ; col++ {
				v, exists := grid[lib.Position{row, col}]
				if !exists {
					continue root
				}
				if v {
					break
				}
			}

			for ; ; col++ {
				if col >= maxCol {
					break
				}

				found := true
			outer:
				for r := 0; r < squareRow; r++ {
					for c := 0; c < squareCol; c++ {
						if !grid[lib.Position{r + row, c + col}] {
							found = false
							break outer
						}
					}
				}

				if found {
					return col*10000 + row
				}
			}
		}

		maxRow += 100
		maxCol += 50
	}
}