day7.go

package main

import (
	"fmt"
	"strconv"
	"strings"
)

var input = `bn RSHIFT 2 -> bo
lf RSHIFT 1 -> ly
... more input ...`

func main() {
	wires := make(map[string]uint16)

	pile := input
	for {
		pile = parseInput(pile, &wires)
		if pile == "" {
			break
		}

		fmt.Println(wires, len(pile))
	}

	fmt.Println("answer:", wires["a"])
}

func parseInput(in string, wires *map[string]uint16) string {

	getVal := func(key string) (uint16, error) {
		i, err := strconv.Atoi(key)
		if err != nil {
			if a, b := (*wires)[key]; b {
				return a, nil
			} else {
				return 0, fmt.Errorf("undefined")
			}
		}

		return uint16(i), nil
	}

	pile := ""

	sets := strings.Split(in, "\n")
	for _, set := range sets {
		parts := strings.Split(set, " ")
		num := len(parts)

		if num == 3 {
			a, err1 := getVal(parts[0])
			if err1 != nil {
				pile += set + "\n"
				continue
			}

			(*wires)[parts[2]] = a
		} else if num == 4 {
			a, err1 := getVal(parts[1])
			if err1 != nil {
				pile += set + "\n"
				continue
			}

			switch parts[0] {
			case "NOT":
				(*wires)[parts[3]] = ^a
			default:
				panic("unhandled operator")
			}

		} else if num == 5 {

			a, err1 := getVal(parts[0])
			b, err2 := getVal(parts[2])
			if err1 != nil || err2 != nil {
				pile += set + "\n"
				continue
			}

			switch parts[1] {
			case "AND":
				(*wires)[parts[4]] = a & b
				break
			case "OR":
				(*wires)[parts[4]] = a | b
				break
			case "LSHIFT":
				(*wires)[parts[4]] = a << b
				break
			case "RSHIFT":
				(*wires)[parts[4]] = a >> b
				break
			default:
				panic("unhandled operator")
			}

		} else {
			panic("unhandled size")
		}
	}

	return strings.TrimSpace(pile)
}