Feat: Perfect number algorithm

src/main/java/com/williamfiset/algorithms/math/PerfectNumber.java

@@ -0,0 +1,18 @@
+package com.williamfiset.algorithms.math;
+
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+
+public class PerfectNumber {
+    public static boolean isPerfect(int n) {
+        if(n <= 1) return false;
+
+        return IntStream.range(1, n / 2 + 1).filter(i -> n % i == 0).sum() == n;
+    }
+
+    public static boolean isPerfect(long n) {
+        if(n <= 1L) return false;
+
+        return LongStream.range(1, n / 2 + 1).filter(i -> n % i == 0).sum() == n;
+    }
+}

src/test/java/com/williamfiset/algorithms/math/PerfectNumberTest.java

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+package com.williamfiset.algorithms.math;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Random;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static com.williamfiset.algorithms.math.PerfectNumber.isPerfect;
+
+class PerfectNumberTest {
+    private final Random random = new Random();
+
+    @Test
+    void testIsPerfect() {
+        assertFalse(isPerfect(random.nextInt(Integer.MIN_VALUE, 6)));
+        assertFalse(isPerfect(random.nextLong(Long.MIN_VALUE, 6L)));
+
+        assertTrue(isPerfect(6));
+        assertTrue(isPerfect(6L));
+
+        assertFalse(isPerfect(random.nextInt(7, 28)));
+        assertFalse(isPerfect(random.nextLong(7L, 28L)));
+
+        assertTrue(isPerfect(28));
+        assertTrue(isPerfect(28L));
+
+        assertFalse(isPerfect(random.nextInt(29, 8128)));
+        assertFalse(isPerfect(random.nextLong(29L, 8128L)));
+
+        assertTrue(isPerfect(8128));
+        assertTrue(isPerfect(8128L));
+
+        assertFalse(isPerfect(random.nextInt(8129, 33550336)));
+        assertFalse(isPerfect(random.nextLong(8129L, 33550336L)));
+
+        assertTrue(isPerfect(33550336));
+        assertTrue(isPerfect(33550336L));
+    }
+}