From 58b9f0bb0cf4827eec13ca2129f8936497edc7e3 Mon Sep 17 00:00:00 2001
From: shellhub <shellhub.me@gmail.com>
Date: Fri, 11 Oct 2019 16:44:33 +0800
Subject: [PATCH] perfect number

---
 Maths/PerfectNumber.java | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Maths/PerfectNumber.java

diff --git a/Maths/PerfectNumber.java b/Maths/PerfectNumber.java
new file mode 100644
index 00000000..ceaf0b2b
--- /dev/null
+++ b/Maths/PerfectNumber.java
@@ -0,0 +1,33 @@
+package Maths;
+
+/**
+ * In number theory, a perfect number is a positive integer that is equal to the sum of
+ * its positive divisors, excluding the number itself. For instance, 6 has divisors 1, 2 and 3
+ * (excluding itself), and 1 + 2 + 3 = 6, so 6 is a perfect number.
+ * <p>
+ * link:https://en.wikipedia.org/wiki/Perfect_number
+ * </p>
+ */
+public class PerfectNumber {
+    public static void main(String[] args) {
+        assert isPerfectNumber(6); /* 1 + 2 + 3 == 6 */
+        assert !isPerfectNumber(8); /* 1 + 2 + 4 != 8 */
+        assert isPerfectNumber(28); /* 1 + 2 + 4 + 7 + 14 == 28 */
+    }
+
+    /**
+     * Check if {@code number} is perfect number or not
+     *
+     * @param number the number
+     * @return {@code true} if {@code number} is perfect number, otherwise false
+     */
+    public static boolean isPerfectNumber(int number) {
+        int sum = 0;  /* sum of its positive divisors */
+        for (int i = 1; i < number; ++i) {
+            if (number % i == 0) {
+                sum += i;
+            }
+        }
+        return sum == number;
+    }
+}