benchstat.txt

❯ benchstat v3.txt v4_garman_bytes.txt
name      old time/op  new time/op  delta
Answer-8   136ns ± 0%    23ns ± 0%  -83.28%  (p=0.016 n=4+5)

❯ benchstat v4_fugi.txt v4_garman_bytes.txt
name      old time/op  new time/op  delta
Answer-8  37.8ns ± 0%  22.8ns ± 0%  -39.66%  (p=0.008 n=5+5)

main.go

package main

import (
	"fmt"
	"io/ioutil"
	"os"
	"strings"
)

func main() {
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func run() error {
	input, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		return err
	}
	answer, err := Answer(strings.TrimSpace(string(input)))
	fmt.Printf("answer: %v\n", answer)
	return err
}

func Answer(input string) (int, error) {
	increases := -1

	var prev, intVal int64
	for _, c := range []byte(input) {
		if c != '\n' {
			intVal = intVal*255 + int64(c)
		} else {
			if intVal > prev {
				increases++
			}
			prev = intVal
			intVal = 0
		}
	}
	if intVal > prev {
		increases++
	}

	return increases, nil
}