From 8b1bf8619f7ea63318b1f9f6d205f3e5930b073f Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Wed, 4 Nov 2020 09:56:19 +0800
Subject: [PATCH] 34: digit factorials

---
 34_digit_factorials/main.go      |  43 ++++++++++++
 34_digit_factorials/main_test.go | 108 +++++++++++++++++++++++++++++++
 2 files changed, 151 insertions(+)
 create mode 100644 34_digit_factorials/main.go
 create mode 100644 34_digit_factorials/main_test.go

diff --git a/34_digit_factorials/main.go b/34_digit_factorials/main.go
new file mode 100644
index 0000000..14b4992
--- /dev/null
+++ b/34_digit_factorials/main.go
@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	sum := 0
+	max := factorialOf(9) * 10
+	for i := 3; i < max; i++ {
+		if sumNumberFactorials(splitNumber(i)) == i {
+			sum += i
+		}
+	}
+	fmt.Println("sum:", sum)
+}
+
+func sumNumberFactorials(ns []int) int {
+	sum := 0
+	for _, n := range ns {
+		sum += factorialOf(n)
+	}
+	return sum
+}
+
+func splitNumber(n int) []int {
+	var ret []int
+	str := strconv.Itoa(n)
+	for _, c := range str {
+		i, _ := strconv.Atoi(string(c))
+		ret = append(ret, i)
+	}
+	return ret
+}
+
+func factorialOf(n int) int {
+	p := 1
+	for i := n; i > 0; i-- {
+		p *= i
+	}
+	return p
+}
diff --git a/34_digit_factorials/main_test.go b/34_digit_factorials/main_test.go
new file mode 100644
index 0000000..25762df
--- /dev/null
+++ b/34_digit_factorials/main_test.go
@@ -0,0 +1,108 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_factorialOf(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tt := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			"1",
+			args{1},
+			1,
+		},
+		{
+			"2",
+			args{2},
+			2,
+		},
+		{
+			"4",
+			args{4},
+			24,
+		},
+		{
+			"10",
+			args{10},
+			3628800,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := factorialOf(tc.args.n); got != tc.want {
+				t.Errorf("factorialOf() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func Test_splitNumber(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tt := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{
+			"13",
+			args{13},
+			[]int{1, 3},
+		},
+		{
+			"123",
+			args{123},
+			[]int{1, 2, 3},
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := splitNumber(tc.args.n); !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("splitNumber() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
+func Test_sumNumberFactorials(t *testing.T) {
+	type args struct {
+		ns []int
+	}
+	tt := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			"1",
+			args{[]int{1}},
+			1,
+		},
+		{
+			"12",
+			args{[]int{1, 2}},
+			3,
+		},
+		{
+			"123",
+			args{[]int{1, 2, 3}},
+			9,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := sumNumberFactorials(tc.args.ns); got != tc.want {
+				t.Errorf("sumNumberFactorials() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}