prime factors 210915

prime_factors_210915/main_test.go

@@ -0,0 +1,50 @@
+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 * 5 * 11 * 37 * 73, []int{2, 2, 5, 11, 37, 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 = %v, want %v", tc.input, got, tc.want)
+			}
+		})
+	}
+}
+
+func PrimeFactorsOf(n int) []int {
+	ret := make([]int, 0)
+	d := 2
+	for d < n {
+		for n % d == 0 {
+			ret = append(ret, d)
+			n /= d
+		}
+		d++
+	}
+	if n > 1 {
+		ret = append(ret, n)
+	}
+	return ret
+}