0.result.txt

$ go test -bench=. -benchmem
PASS
BenchmarkAnswer3	 1000000	      1248 ns/op	     344 B/op	       6 allocs/op
BenchmarkAnswer4	 2000000	       836 ns/op	     128 B/op	       1 allocs/op

pi_test.go

package main

import (
	"reflect"
	"testing"
)

var sentence string = "Now I need a drink, alcoholic of course, after the heavy lectures involving quantum mechanics."
var expect = []int{3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9}

func answer3(sentence string) []int {
	var pi []int
	var prev, i int
	b := []byte(sentence)
	l := len(b)
	for i < l {
		for ; i < l; i++ {
			if ('a' <= b[i] && b[i] <= 'z') || ('A' <= b[i] && b[i] <= 'Z') {
				break
			}
		}
		if i < l {
			prev = i
			for ; i < l; i++ {
				if !(('a' <= b[i] && b[i] <= 'z') || ('A' <= b[i] && b[i] <= 'Z')) {
					break
				}
			}
			pi = append(pi, i-prev)
		}
		i++
	}

	return pi

}

func answer4(s string) []int {
	res := make([]int, 0, len(s)/6)
	cnt := 0
	for _, c := range s {
		switch {
		case 'a' <= c && c <= 'z', 'A' <= c && c <= 'Z':
			cnt++
		default:
			if cnt != 0 {
				res = append(res, cnt)
				cnt = 0
			}
		}
	}
	if cnt != 0 {
		res = append(res, cnt)
		cnt = 0
	}
	return res
}

func TestAnswer3(t *testing.T) {
	ans := answer3(sentence)
	if !reflect.DeepEqual(ans, expect) {
		t.Errorf("%+v", ans)
	}
}

func BenchmarkAnswer3(b *testing.B) {
	for i := 0; i < b.N; i++ {
		answer3(sentence)
	}
}
func TestAnswer4(t *testing.T) {
	ans := answer4(sentence)
	if !reflect.DeepEqual(ans, expect) {
		t.Errorf("%+v", ans)
	}
}

func BenchmarkAnswer4(b *testing.B) {
	for i := 0; i < b.N; i++ {
		answer4(sentence)
	}
}