Prime factors

README.md

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 # codekata
- code kat
+This is the code kata for golang. 
+Code Kata is an attempt to bring this element of practice to software development. A kata is an exercise in karate where you repeat a form many, many times, making little improvements in each. 
+The intent behind code kata is similar. Each is a short exercise (perhaps 30 minutes to an hour long). Some involve programming, and can be coded in many different ways.

go.mod

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+module github.com/vicren/codekata_golang
+
+go 1.13

prime_factors/README.md

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+# Prime factors
+
+Prime Numbers kata calculates the prime numbers up to 100.
+
+Example:
+
+The prime numbers to 10 are 2, 3, 5, 7.
+
+Clarifying Notes:
+
+A prime number is a integer which is only divisible by itself and 1.

prime_factors/prime_factors.go

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+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("prime number up to 100 is:")
+	for i := 0; i < 101; i++ {
+		pf := PrimeFactorsOf(i)
+		if len(pf) < 2 {
+			fmt.Println(i)
+		}
+	}
+}
+
+func PrimeFactorsOf(n int) []int {
+	ret := make([]int, 0)
+	divider := 2
+	for divider < n {
+		for n%divider == 0 {
+			ret = append(ret, divider)
+			n /= divider
+		}
+		divider++
+	}
+	if n > 1 {
+		ret = append(ret, n)
+	}
+	return ret
+}

prime_factors/prime_factors_test.go

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+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestPrimeFactorsOf(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  []int
+	}{
+		{
+			"prime factors of 1",
+			1,
+			[]int{},
+		},
+		{
+			"prime factors of 2",
+			2,
+			[]int{2},
+		},
+		{
+			"prime factors of 3",
+			3,
+			[]int{3},
+		},
+		{
+			"prime factors of 1",
+			1,
+			[]int{},
+		},
+		{
+			"prime factors of 2",
+			2,
+			[]int{2},
+		},
+		{
+			"prime factors of 4",
+			4,
+			[]int{2, 2},
+		},
+		{
+			"prime factors of 5",
+			5,
+			[]int{5},
+		},
+		{
+			"prime factors of 6",
+			6,
+			[]int{2, 3},
+		},
+		{
+			"prime factors of 7",
+			7,
+			[]int{7},
+		},
+		{
+			"prime factors of 8",
+			8,
+			[]int{2, 2, 2},
+		},
+		{
+			"prime factors of 9",
+			9,
+			[]int{3, 3},
+		},
+		{
+			"prime factors of a big number",
+			2 * 2 * 2 * 3 * 3 * 5 * 7 * 11 * 13 * 73,
+			[]int{2, 2, 2, 3, 3, 5, 7, 11, 13, 73},
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := PrimeFactorsOf(tc.input)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("PrimeFactorsOf %d, got %v, want %v", tc.input, got, tc.want)
+			}
+		})
+	}
+}