package main

import (
	"io/ioutil"
	"regexp"
)

func AppendByte(slice []byte, data ...byte) []byte {
	m := len(slice)
	n := m + len(data)
	if n > cap(slice) { // if necessary, reallocate
		// allocate double what's needed, for future growth.
		newSlice := make([]byte, (n+1)*2)
		copy(newSlice, slice)
		slice = newSlice
	}
	slice = slice[0:n]
	copy(slice[m:n], data)
	return slice
}

// STOP OMIT

// Filter returns a new slice holding only
// the elements of s that satisfy f()
func Filter(s []int, fn func(int) bool) []int {
	var p []int // == nil
	for _, i := range s {
		if fn(i) {
			p = append(p, i)
		}
	}
	return p
}

// STOP OMIT

var digitRegexp = regexp.MustCompile("[0-9]+")

func FindDigits(filename string) []byte {
	b, _ := ioutil.ReadFile(filename)
	return digitRegexp.Find(b)
}

// STOP OMIT

func CopyDigits(filename string) []byte {
	b, _ := ioutil.ReadFile(filename)
	b = digitRegexp.Find(b)
	c := make([]byte, len(b))
	copy(c, b)
	return c
}

// STOP OMIT