Rule 110 in Go

rule110.go

package main

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

// Copyright (C) 2023  Gabriel de Brito

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

func readline(prompt string) string {
	fmt.Print(prompt)
	stdin := bufio.NewScanner(os.Stdin)
	stdin.Scan()
	return stdin.Text()
}

func readint(prompt string) int {
	for {
		i, err := strconv.Atoi(readline(prompt))
		if nil == err && 0 <= i {
			return i
		}
		fmt.Println("please enter a valid positive integer!")
	}
}

func is_binary(s string) bool {
	for _, c := range s {
		if '0' != c && '1' != c {
			return false
		}
	}
	return true
}

func readBinaryString(prompt string) string {
	for {
		s := readline(prompt)
		if is_binary(s) {
			return s
		}
		fmt.Println("please enter a string of only 1 and 0!")
	}
}

func applyRule110_chars(bef byte, act byte, aft byte) string {
	arr := [3]byte{bef, act, aft}
	switch {
	case [3]byte{'1', '1', '1'} == arr:
		return "0"
	case [3]byte{'1', '1', '0'} == arr:
		return "1"
	case [3]byte{'1', '0', '1'} == arr:
		return "1"
	case [3]byte{'1', '0', '0'} == arr:
		return "0"
	case [3]byte{'0', '1', '1'} == arr:
		return "1"
	case [3]byte{'0', '1', '0'} == arr:
		return "1"
	case [3]byte{'0', '0', '1'} == arr:
		return "1"
	case [3]byte{'0', '0', '0'} == arr:
		return "0"
	}

	return "0"
}

func applyRule110(s string) string {
	next := applyRule110_chars('0', s[0], s[1])
	for i := 1; len(s)-1 > i; i++ {
		next += applyRule110_chars(s[i-1], s[i], s[i+1])
	}
	next += applyRule110_chars(s[len(s)-2], s[len(s)-1], '0')
	return next
}

func main() {
	fmt.Printf("===\nRule 110\n===\n")
	n := readint("number of iterations: ")
	s := readBinaryString("initial state: ")
	fmt.Println(s)
	for n := n; 0 <= n; n-- {
		s = applyRule110(s)
		for _, c := range s {
			if '0' == c {
				fmt.Print(" ")
			} else {
				fmt.Print("1")
			}
		}
		fmt.Println()
	}
	fmt.Println(s)
}