Prime factors 210827

prime_factors_210827/prime_factors_test.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestPrimeFactorsOf(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  []int
+	}{
+		{
+			"1",
+			1,
+			[]int{},
+		},
+		{
+			"2",
+			2,
+			[]int{2},
+		},
+		{
+			"3",
+			3,
+			[]int{3},
+		},
+		{
+			"4",
+			4,
+			[]int{2, 2},
+		},
+		{
+			"5",
+			5,
+			[]int{5},
+		},
+		{
+			"6",
+			6,
+			[]int{2, 3},
+		},
+		{
+			"7",
+			7,
+			[]int{7},
+		},
+		{
+			"8",
+			8,
+			[]int{2, 2, 2},
+		},
+		{
+			"9",
+			9,
+			[]int{3, 3},
+		},
+		{
+			"a very large number",
+			2 * 2 * 2 * 3 * 5 * 7 * 11 * 23 * 37,
+			[]int{2, 2, 2, 3, 5, 7, 11, 23, 37},
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := PrimeFactorsOf(tc.input)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("Prime Factors of %d = %v, want %v", tc.input, got, tc.want)
+			}
+		})
+	}
+}
+
+func PrimeFactorsOf(n int) []int {
+	var ret = make([]int, 0)
+	divider := 2
+	for divider < n {
+		for n%divider == 0 {
+			ret = append(ret, divider)
+			n = n / divider
+		}
+		divider++
+	}
+	if n > 1 {
+		ret = append(ret, n)
+	}
+	return ret
+}