atoi_itoa.go

package atoi_itoa

import (
	"fmt"
	"regexp"
)

func atoi(s string) (int, error) {
	re := regexp.MustCompile(`^-?\d+$`)

	if !re.MatchString(s) {
		return 0, fmt.Errorf("'%s' is not a valid number")
	}

	var negative bool

	if runes := []rune(s); runes[0] == '-' {
		negative = true
		s = string(runes[1:])
	}

	result := 0

	for _, r := range s {
		result *= 10
		result += int(r - '0')
	}

	if negative {
		return -result, nil
	}

	return result, nil
}

func itoa(i int) string {
	if i == 0 {
		return "0"
	}

	result := make([]rune, 0)
	var negative bool

	if i < 0 {
		negative = true
		i = -i
	}

	for n := i; n > 0; n /= 10 {
		result = append(result, '0'+rune(n%10))
	}

	if negative {
		result = append(result, '-')
	}

	for i, j := 0, len(result)-1; i < j; i, j = i+1, j-1 {
		result[i], result[j] = result[j], result[i]
	}

	return string(result)
}

atoi_itoa_test.go

package atoi_itoa

import "testing"

func TestAtoiZero(t *testing.T) {
	actual, err := atoi("0")
	expected := 0

	if err != nil {
		t.Error(err)
	}

	if actual != expected {
		t.Errorf("%d != %d", actual, expected)
	}
}

func TestAtoiOne(t *testing.T) {
	actual, err := atoi("1")
	expected := 1

	if err != nil {
		t.Error(err)
	}

	if actual != expected {
		t.Errorf("%d != %d", actual, expected)
	}
}

func TestAtoiLongerNumbers(t *testing.T) {
	actual, err := atoi("123890")
	expected := 123890

	if err != nil {
		t.Error(err)
	}

	if actual != expected {
		t.Errorf("%d != %d", actual, expected)
	}
}

func TestAtoiNegativeNumbers(t *testing.T) {
	actual, err := atoi("-123890")
	expected := -123890

	if err != nil {
		t.Error(err)
	}

	if actual != expected {
		t.Errorf("%d != %d", actual, expected)
	}
}

func TestAtoiInvalidInput(t *testing.T) {
	input := "abc"
	_, err := atoi(input)

	if err == nil {
		t.Errorf("%s is not valid input", input)
	}

	input = "--123"
	_, err = atoi(input)

	if err == nil {
		t.Errorf("%s is not valid input", input)
	}

}

func TestItoaZero(t *testing.T) {
	actual := itoa(0)
	expected := "0"

	if actual != expected {
		t.Errorf("%s != %s", actual, expected)
	}
}

func TestItoaOne(t *testing.T) {
	actual := itoa(1)
	expected := "1"

	if actual != expected {
		t.Errorf("%s != %s", actual, expected)
	}
}

func TestItoaLongerNumbers(t *testing.T) {
	actual := itoa(12300890)
	expected := "12300890"

	if actual != expected {
		t.Errorf("%s != %s", actual, expected)
	}
}

func TestItoaNegativeNumbers(t *testing.T) {
	actual := itoa(-12300890)
	expected := "-12300890"

	if actual != expected {
		t.Errorf("%s != %s", actual, expected)
	}
}