From 37a1659e18ab5156c88b6897eeaf1f599d63efcd Mon Sep 17 00:00:00 2001
From: Taranjeet Singh Kalsi <taranjeetkalsi15@gmail.com>
Date: Thu, 3 Nov 2022 18:29:13 +0530
Subject: [PATCH] Add HarshadNumberTest (#3722)

---
 .../thealgorithms/maths/HarshadNumber.java    | 69 ++++++++-----------
 .../maths/HarshadNumberTest.java              | 23 +++++++
 2 files changed, 53 insertions(+), 39 deletions(-)
 create mode 100644 src/test/java/com/thealgorithms/maths/HarshadNumberTest.java

diff --git a/src/main/java/com/thealgorithms/maths/HarshadNumber.java b/src/main/java/com/thealgorithms/maths/HarshadNumber.java
index 9b24209bf..b30ada488 100644
--- a/src/main/java/com/thealgorithms/maths/HarshadNumber.java
+++ b/src/main/java/com/thealgorithms/maths/HarshadNumber.java
@@ -1,56 +1,47 @@
-// Wikipedia for Harshad Number : https://en.wikipedia.org/wiki/Harshad_number
 package com.thealgorithms.maths;
 
-import java.util.Scanner;
+// Wikipedia for Harshad Number : https://en.wikipedia.org/wiki/Harshad_number
 
 public class HarshadNumber {
 
-    public static void main(String[] args) {
-        Scanner sc = new Scanner(System.in);
-        System.out.print("Enter a number : ");
-        long a = sc.nextLong();
+    /**
+     * A function to check if a number is Harshad number or not
+     *
+     * @param n The number to be checked
+     * @return {@code true} if {@code a} is Harshad number, otherwise
+     *         {@code false}
+     */
+    public static boolean isHarshad(long n) {
+        if (n <= 0)
+            return false;
 
-        checkHarshadNumber(a);
+        long t = n;
+        int sumOfDigits = 0;
+        while (t > 0) {
+            sumOfDigits += t % 10;
+            t /= 10;
+        }
+
+        return n % sumOfDigits == 0;
     }
 
     /**
      * A function to check if a number is Harshad number or not
      *
-     * @param a The number which should be checked
+     * @param s The number in String to be checked
+     * @return {@code true} if {@code a} is Harshad number, otherwise
+     *         {@code false}
      */
-    public static void checkHarshadNumber(long a) {
-        long b = a;
-        int sum = 0;
+    public static boolean isHarshad(String s) {
+        long n = Long.valueOf(s);
+        if (n <= 0)
+            return false;
 
-        // this is just for showing the explanation else it's of no use you can ommit it
-        int[] each = new int[Long.toString(a).length()];
-
-        int c = 0;
-
-        while (b > 0) {
-            sum += b % 10;
-            each[c] = (int) (b % 10);
-            b /= 10;
-            c++;
+        int sumOfDigits = 0;
+        for (char ch : s.toCharArray()) {
+            sumOfDigits += ch - '0';
         }
 
-        if (a % sum == 0) {
-            System.out.println(a + " is a Harshad Number");
-
-            // For you better explanation how is that a Harshad Number
-            System.out.println("\nExplaination :");
-
-            for (int i = each.length - 1; i >= 0; i--) {
-                System.out.print(each[i] + " ");
-                if (i != 0) {
-                    System.out.print("+ ");
-                }
-            }
-
-            System.out.println("= " + sum);
-            System.out.println(sum + " × " + (a / sum) + " = " + a);
-        } else {
-            System.out.println(a + " is not a Harshad Number");
-        }
+        return n % sumOfDigits == 0;
     }
 }
diff --git a/src/test/java/com/thealgorithms/maths/HarshadNumberTest.java b/src/test/java/com/thealgorithms/maths/HarshadNumberTest.java
new file mode 100644
index 000000000..f9176961f
--- /dev/null
+++ b/src/test/java/com/thealgorithms/maths/HarshadNumberTest.java
@@ -0,0 +1,23 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+public class HarshadNumberTest {
+
+    @Test
+    public void harshadNumber() {
+        
+        assertTrue(HarshadNumber.isHarshad(18));
+        assertFalse(HarshadNumber.isHarshad(-18));
+        assertFalse(HarshadNumber.isHarshad(19));
+        assertTrue(HarshadNumber.isHarshad(999999999));
+        assertFalse(HarshadNumber.isHarshad(0));
+
+        assertTrue(HarshadNumber.isHarshad("18"));
+        assertFalse(HarshadNumber.isHarshad("-18"));
+        assertFalse(HarshadNumber.isHarshad("19"));
+        assertTrue(HarshadNumber.isHarshad("999999999"));
+        assertTrue(HarshadNumber.isHarshad("99999999999100"));
+    }
+}