bench.out

PASS
BenchmarkConvertA	  300000	      5625 ns/op
BenchmarkConvertB	  300000	      5756 ns/op
ok  	_/home/benjica/exercism/go/raindrops	3.532s

raindrops.go

package raindrops

import "fmt"

func Convert(num int) string {
	return ConvertCompare(num, "A")
}

func ConvertCompare(num int, compare string) string {

	// We build a map of the language
	// We have to preserve order so slices are required
	words := []string{"Pling", "Plang", "Plong"}
	factors := []int{3, 5, 7}

	if compare == "A" {
		return ConvertFactorMapA(num, words, factors)
	} else {
		return ConvertFactorMapB(num, words, factors)
	}
}

func ConvertFactorMapA(num int, words []string, factors []int) string {

	var speak string

	// Determine if given num is composed of any of the factors
	for i, factor := range factors {
		if num%factor == 0 {
			speak += fmt.Sprintf(words[i])
		}
	}

	// If string was not modified by map, emit num
	if len(speak) == 0 {
		speak += fmt.Sprintf("%d", num)
	}

	return speak
}

func ConvertFactorMapB(num int, words []string, factors []int) string {

	var speak string

	// Determine if given num is composed of any of the factors
	for i, factor := range factors {
		if num%factor == 0 {
			speak += fmt.Sprintf(words[i])
		}
	}

	// If string was not modified by map, emit num
	if speak == "" {
		speak += fmt.Sprintf("%d", num)
	}

	return speak
}

raindrops_test.go

package raindrops

import "testing"

var tests = []struct {
	input    int
	expected string
}{
	{1, "1"},
	{3, "Pling"},
	{5, "Plang"},
	{7, "Plong"},
	{6, "Pling"},
	{9, "Pling"},
	{10, "Plang"},
	{14, "Plong"},
	{15, "PlingPlang"},
	{21, "PlingPlong"},
	{25, "Plang"},
	{35, "PlangPlong"},
	{49, "Plong"},
	{52, "52"},
	{105, "PlingPlangPlong"},
	{12121, "12121"},
}

func TestConvert(t *testing.T) {
	for _, test := range tests {
		if actual := Convert(test.input); actual != test.expected {
			t.Errorf("Convert(%d) = %q, expected %q.",
				test.input, actual, test.expected)
		}
	}
}

func BenchmarkConvertA(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, test := range tests {
			ConvertCompare(test.input, "A")
		}
	}
}

func BenchmarkConvertB(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, test := range tests {
			ConvertCompare(test.input, "B")
		}
	}
}