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", 17 * 71 * 73 * 113, []int{17, 71, 73, 113}},
	}

	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
}