adventofcode/2017/day16/day16.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

func main() {
	var progs string
	length := 16
	iters := 1000000000
	if len(os.Args) > 1 {
		length = Atoi(os.Args[1])
		if len(os.Args) > 2 {
			iters = Atoi(os.Args[2])
		}
	}

	// Create a starting string
	for i := 0; i < length; i++ {
		progs += string('a' + i)
	}

	inp := StdinToString()
	moves := strings.Split(inp, ",")

	var loopEnd int
	var state []string
	doneProgs := progs
	state = append(state, progs)
	for loopEnd = 1; loopEnd < (iters / 2); loopEnd++ {
		doneProgs = doDance(doneProgs, moves)
		state = append(state, doneProgs)
		if doneProgs == progs {
			fmt.Println("Loops at", loopEnd)
			pos := (iters / loopEnd) * loopEnd
			fmt.Println("Final State", state[iters-pos])
			break
		}
	}
}

func doDance(progs string, moves []string) string {
	for _, v := range moves {
		switch v[0] {
		case 's':
			progs = Spin(progs, Atoi(v[1:]))
		case 'p':
			pts := strings.Split(v[1:], "/")
			progs = Partner(progs, pts[0], pts[1])
		case 'x':
			pts := strings.Split(v[1:], "/")
			progs = Exchange(progs, Atoi(pts[0]), Atoi(pts[1]))
		}
	}
	return progs
}

func Spin(progs string, cnt int) string {
	stSpin := len(progs) - cnt
	return progs[stSpin:] + progs[:stSpin]
}

func Exchange(progs string, i1, i2 int) string {
	if i1 > i2 {
		i1, i2 = i2, i1
	}
	return progs[:i1] + string(progs[i2]) + progs[i1+1:i2] + string(progs[i1]) + progs[i2+1:]
}

func Partner(progs string, p1, p2 string) string {
	return Exchange(progs, strings.Index(progs, p1), strings.Index(progs, p2))
}

func StdinToString() string {
	var input string
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		input = scanner.Text()
	}
	return input
}

func Atoi(i string) int {
	var ret int
	var err error
	if ret, err = strconv.Atoi(i); err != nil {
		log.Fatal("Invalid Atoi")
	}
	return ret
}