Add prime factorization algorithm (TheAlgorithms#3278)

itsAkshayDubey · web-flow · commit 07a5531f1a7b · 2022-09-21T19:29:20.000Z
diff --git a/src/main/java/com/thealgorithms/maths/PrimeFactorization.java b/src/main/java/com/thealgorithms/maths/PrimeFactorization.java
@@ -1,35 +1,39 @@
 package com.thealgorithms.maths;
 
-import java.util.Scanner;
+/*
+ * Authors: 
+ * (1) Aitor Fidalgo S&aacute;nchez (https://github.com/aitorfi) 
+ * (2) Akshay Dubey (https://github.com/itsAkshayDubey)
+*/
+
+import java.util.ArrayList;
+import java.util.List;
 
 public class PrimeFactorization {
 
-    public static void main(String[] args) {
-        System.out.println("## all prime factors ##");
-        Scanner scanner = new Scanner(System.in);
-        System.out.print("Enter a number: ");
-        int n = scanner.nextInt();
-        System.out.print(("printing factors of " + n + " : "));
-        pfactors(n);
-        scanner.close();
-    }
-
-    public static void pfactors(int n) {
-
-        while (n % 2 == 0) {
-            System.out.print(2 + " ");
-            n /= 2;
-        }
-
-        for (int i = 3; i <= Math.sqrt(n); i += 2) {
-            while (n % i == 0) {
-                System.out.print(i + " ");
-                n /= i;
-            }
-        }
-
-        if (n > 2) {
-            System.out.print(n);
-        }
-    }
+	public static List<Integer> pfactors(int n) {
+		
+		List<Integer> primeFactors = new ArrayList<>();
+
+		if (n == 0) {
+			return primeFactors;
+		}
+
+		while (n % 2 == 0) {
+			primeFactors.add(2);
+			n /= 2;
+		}
+
+		for (int i = 3; i <= Math.sqrt(n); i += 2) {
+			while (n % i == 0) {
+				primeFactors.add(i);
+				n /= i;
+			}
+		}
+
+		if (n > 2) {
+			primeFactors.add(n);
+		}
+		return primeFactors;
+	}
 }
diff --git a/src/test/java/com/thealgorithms/maths/PrimeFactorizationTest.java b/src/test/java/com/thealgorithms/maths/PrimeFactorizationTest.java
@@ -0,0 +1,36 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+class PrimeFactorizationTest {
+
+	@Test
+	void testpFactorsMustReturnEmptyList() {
+		//given
+		int n = 0; 
+		
+		//then
+		assertTrue(PrimeFactorization.pfactors(n).isEmpty());
+	}
+	
+	@Test
+	void testpFactorsMustReturnNonEmptyList() {
+		//given
+		int n = 198;
+		int expectedListSize = 4;
+		
+		//when
+		List<Integer> actualResultList = PrimeFactorization.pfactors(n);
+		
+		//then
+		assertEquals(expectedListSize, actualResultList.size());
+		assertEquals(2, actualResultList.get(0));
+		assertEquals(3, actualResultList.get(1));
+		assertEquals(3, actualResultList.get(2));
+		assertEquals(11, actualResultList.get(3));
+	}
+}
