From d2e6a7d798fad2fc13e9481cd7d7c5963d158dfe Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Thu, 9 Sep 2021 10:04:13 +0800
Subject: [PATCH] prime factors 210909

---
 prime_factors_210909/main_test.go | 50 +++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 prime_factors_210909/main_test.go

diff --git a/prime_factors_210909/main_test.go b/prime_factors_210909/main_test.go
new file mode 100644
index 0000000..d27e5fd
--- /dev/null
+++ b/prime_factors_210909/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 vary large number", 2 * 3 * 5 * 7 * 11 * 13 * 31 * 71, []int{2, 3, 5, 7, 11, 13, 31, 71}},
+	}
+
+	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 {
+	var 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
+}