add prime factors

realDuYuanChao · realDuYuanChao · commit 283ad780f7a5 · 2020-10-09T16:51:26.000+08:00
diff --git a/src/main/java/com/examplehub/maths/PrimeFactors.java b/src/main/java/com/examplehub/maths/PrimeFactors.java
@@ -0,0 +1,32 @@
+package com.examplehub.maths;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PrimeFactors {
+
+    /**
+     * Get all prime factors of a number.
+     *
+     * @param number the number to be calculated.
+     * @return all prime factors.
+     */
+    public static int[] primeFactors(int number) {
+        List<Integer> integers = new ArrayList<>();
+        while (number % 2 == 0) {
+            integers.add(2);
+            number >>= 1;
+        }
+
+        for (int i = 3; i <= Math.sqrt(number); i += 2) {
+            while (number % i == 0) {
+                integers.add(i);
+                number /= i;
+            }
+        }
+        if (number > 2) {
+            integers.add(number);
+        }
+        return integers.stream().mapToInt(i -> i).toArray();
+    }
+}
diff --git a/src/test/java/com/examplehub/maths/PrimeFactorsTest.java b/src/test/java/com/examplehub/maths/PrimeFactorsTest.java
@@ -0,0 +1,17 @@
+package com.examplehub.maths;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class PrimeFactorsTest {
+
+    @Test
+    void testPrimeFactors() {
+        assertTrue(Arrays.equals(new int[]{2}, PrimeFactors.primeFactors(2)));
+        assertTrue(Arrays.equals(new int[]{2, 2, 3}, PrimeFactors.primeFactors(12)));
+        assertTrue(Arrays.equals(new int[]{3, 3, 5, 7}, PrimeFactors.primeFactors(315)));
+    }
+}
