7.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"regexp"
	"strconv"
)

var (
	r        = regexp.MustCompile(`([a-z0-9]+)? ?([A-Z]+)? ?([0-9]+)? ?([a-z0-9]+)? -> ([a-z]+)`)
	wireVals = map[string]int16{}
	ops      = []*Operation{}
)

type Operation struct {
	Name  string
	Left  string
	Right string
	Arg   string
	Dest  string
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		line := scanner.Text()
		op := parseOperation(line)
		ops = append(ops, op)
	}

	for len(ops) > 0 {
		for i := len(ops) - 1; i >= 0; i-- {
			didEval := evaluate(ops[i])

			if didEval {
				ops = append(ops[:i], ops[i+1:]...)
			}
		}
	}

	fmt.Printf("Value of wire a: %d\n", wireVals["a"])
}

func parseOperation(line string) *Operation {
	result := r.FindStringSubmatch(line)
	return &Operation{
		Name:  result[2],
		Left:  result[1],
		Right: result[4],
		Arg:   result[3],
		Dest:  result[5],
	}
}

func evaluate(op *Operation) bool {
	var lval, rval, result int16
	var hlval, hrval bool

	lval, hlval = resolveOperand(op.Left)
	rval, hrval = resolveOperand(op.Right)

	if !hlval || !hrval {
		return false
	}

	if op.Name == "AND" {
		result = lval & rval
	} else if op.Name == "OR" {
		result = lval | rval
	} else if op.Name == "RSHIFT" {
		shiftArg, _ := strconv.ParseUint(op.Arg, 10, 0)
		result = lval >> shiftArg
	} else if op.Name == "LSHIFT" {
		shiftArg, _ := strconv.ParseUint(op.Arg, 10, 0)
		result = lval << shiftArg
	} else if op.Name == "NOT" {
		result = ^rval
	} else if op.Name == "" {
		result = lval
	}

	//	fmt.Printf("%s %s %s %s -> %s = %d\n", op.Left, op.Name, op.Arg, op.Right, op.Dest, result)
	wireVals[op.Dest] = result
	return true
}

func resolveOperand(val string) (int16, bool) {
	// Operand is empty.  We consider this resolved
	if val == "" {
		return 0, true
	}

	// Value is an integer literal
	val64, err := strconv.ParseInt(val, 10, 16)
	if err == nil {
		return int16(val64), true
	}

	// Check if we have a wire val for this wire name
	if wv, ok := wireVals[val]; ok {
		return wv, true
	}

	// Value is an unresolved wire name
	return 0, false

}