From 9727e555ce3f24466aaccd90fa135f34b350552d Mon Sep 17 00:00:00 2001
From: Timothy Kruger <tjkruger23@gmail.com>
Date: Thu, 12 May 2022 13:52:54 +0200
Subject: [PATCH] BAEL-5563 Reversing a number (#12153)

* BAEL-5563 Reverse a number initial commit

* BAEL-5563 Final improvements before PR

* BAEL-5563 Reverse a number - Draft improvements

* BAEL-5563 Reverse a number - Recursive method improvements

* BAEL-5563 Reverse a number - Recursive method improvements

* BAEL-5563 Reverse a number - Remove unused imports

Co-authored-by: Timothy Kruger - Lenny <gapptechnology@gmail.com>
Co-authored-by: claud <180181@virtualwindow.co.za>
---
 .../baeldung/reversenumber/ReverseNumber.java | 45 +++++++++++++++++++
 .../reversenumber/ReverseNumberUnitTest.java  | 34 ++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 java-numbers-4/src/main/java/com/baeldung/reversenumber/ReverseNumber.java
 create mode 100644 java-numbers-4/src/test/java/com/baeldung/reversenumber/ReverseNumberUnitTest.java

diff --git a/java-numbers-4/src/main/java/com/baeldung/reversenumber/ReverseNumber.java b/java-numbers-4/src/main/java/com/baeldung/reversenumber/ReverseNumber.java
new file mode 100644
index 0000000000..04865a8d52
--- /dev/null
+++ b/java-numbers-4/src/main/java/com/baeldung/reversenumber/ReverseNumber.java
@@ -0,0 +1,45 @@
+package com.baeldung.reversenumber;
+
+public class ReverseNumber {
+
+    public static int reverseNumberWhileLoop(int number) {
+        int reversedNumber = 0;
+        int numberToReverse = Math.abs(number);
+
+        while (numberToReverse > 0) {
+            int mod = numberToReverse % 10;
+            reversedNumber = reversedNumber * 10 + mod;
+            numberToReverse /= 10;
+        }
+
+        return number < 0 ? reversedNumber * -1 : reversedNumber;
+    }
+
+    public static int reverseNumberForLoop(int number) {
+        int reversedNumber = 0;
+        int numberToReverse = Math.abs(number);
+
+        for (; numberToReverse > 0; numberToReverse /= 10) {
+            int mod = numberToReverse % 10;
+            reversedNumber = reversedNumber * 10 + mod;
+        }
+
+        return number < 0 ? reversedNumber * -1 : reversedNumber;
+    }
+
+    public static int reverseNumberRecWrapper(int number) {
+        int output = reverseNumberRec(Math.abs(number), 0);
+        return number < 0 ? output * -1 : output;
+    }
+    private static int reverseNumberRec(int numberToReverse, int recursiveReversedNumber) {
+
+        if (numberToReverse > 0) {
+            int mod = numberToReverse % 10;
+            recursiveReversedNumber = recursiveReversedNumber * 10 + mod;
+            numberToReverse /= 10;
+            return reverseNumberRec(numberToReverse, recursiveReversedNumber);
+        }
+
+        return recursiveReversedNumber;
+    }
+}
diff --git a/java-numbers-4/src/test/java/com/baeldung/reversenumber/ReverseNumberUnitTest.java b/java-numbers-4/src/test/java/com/baeldung/reversenumber/ReverseNumberUnitTest.java
new file mode 100644
index 0000000000..2c55bcc539
--- /dev/null
+++ b/java-numbers-4/src/test/java/com/baeldung/reversenumber/ReverseNumberUnitTest.java
@@ -0,0 +1,34 @@
+package com.baeldung.reversenumber;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ReverseNumberUnitTest {
+
+    private static final int ORIGINAL_NUMBER = 123456789;
+    private static final int REVERSED_NUMBER = 987654321;
+
+    @Test
+    void whenReverseNumberWhileLoop_thenOriginalEqualToReverse() {
+        Assertions.assertThat(ReverseNumber.reverseNumberWhileLoop(ORIGINAL_NUMBER)).isEqualTo(REVERSED_NUMBER);
+    }
+
+    @Test
+    void whenReverseNumberForLoop_thenOriginalEqualToReverse() {
+        Assertions.assertThat(ReverseNumber.reverseNumberForLoop(ORIGINAL_NUMBER)).isEqualTo(REVERSED_NUMBER);
+    }
+
+    @Test
+    void whenReverseNumberRec_thenOriginalEqualToReverse() {
+        Assertions.assertThat(ReverseNumber.reverseNumberRecWrapper(ORIGINAL_NUMBER)).isEqualTo(REVERSED_NUMBER);
+    }
+
+    @Test
+    void whenReverseNegativeNumber_thenNumberShouldReverse() {
+        Assertions.assertThat(ReverseNumber.reverseNumberWhileLoop(ORIGINAL_NUMBER * -1)).isEqualTo(REVERSED_NUMBER * -1);
+        Assertions.assertThat(ReverseNumber.reverseNumberForLoop(ORIGINAL_NUMBER * -1)).isEqualTo(REVERSED_NUMBER * -1);
+        Assertions.assertThat(ReverseNumber.reverseNumberRecWrapper(ORIGINAL_NUMBER * -1)).isEqualTo(REVERSED_NUMBER * -1);
+    }
+}
\ No newline at end of file