From 64d25a8714ac670d1667b078afb81335ea9bbb2b Mon Sep 17 00:00:00 2001
From: VicRen <vic.ren@me.com>
Date: Tue, 20 Oct 2020 15:07:14 +0800
Subject: [PATCH] 21: amicable numbers

---
 21_amicable_numbers/amicable_test.go | 56 ++++++++++++++++++++++++++++
 21_amicable_numbers/main.go          | 34 +++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 21_amicable_numbers/amicable_test.go
 create mode 100644 21_amicable_numbers/main.go

diff --git a/21_amicable_numbers/amicable_test.go b/21_amicable_numbers/amicable_test.go
new file mode 100644
index 0000000..59a684b
--- /dev/null
+++ b/21_amicable_numbers/amicable_test.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"testing"
+)
+
+func Test_sumOfDivisors(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  int
+	}{
+		{
+			"220",
+			220,
+			284,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := sumOfDivisors(tc.input)
+			if got != tc.want {
+				t.Errorf("sumOfDivisors() = %d, want %d", got, tc.want)
+			}
+		})
+	}
+}
+
+func Test_isAmicableNumber(t *testing.T) {
+	tt := []struct {
+		name  string
+		input int
+		want  bool
+	}{
+		{
+			"220",
+			220,
+			true,
+		},
+		{
+			"221",
+			221,
+			false,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			got := isAmicableNumber(tc.input)
+			if got != tc.want {
+				t.Errorf("isAmicableNumber() = %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
diff --git a/21_amicable_numbers/main.go b/21_amicable_numbers/main.go
new file mode 100644
index 0000000..d673161
--- /dev/null
+++ b/21_amicable_numbers/main.go
@@ -0,0 +1,34 @@
+package main
+
+import "fmt"
+
+func main() {
+	var nums []int
+	sum := 0
+	for i := 1; i < 10000; i++ {
+		if isAmicableNumber(i) {
+			nums = append(nums, i)
+			sum += i
+		}
+	}
+	fmt.Println("sum:", sum, "nums:", nums)
+}
+
+func sumOfDivisors(input int) int {
+	sum := 0
+	for i := 1; i <= input/2; i++ {
+		if input%i == 0 {
+			sum += i
+		}
+	}
+	return sum
+}
+
+func isAmicableNumber(input int) bool {
+	da := sumOfDivisors(input)
+	db := sumOfDivisors(da)
+	if da == db {
+		return false
+	}
+	return input == db
+}