From 07945c77042614ae8d86de3048753f990c249f6e Mon Sep 17 00:00:00 2001
From: Himesh Kohad <107066424+HimeshKohad@users.noreply.github.com>
Date: Fri, 11 Aug 2023 17:52:14 +0530
Subject: [PATCH] Add StrobogrammaticNumber (#4278)

---
 .../maths/StrobogrammaticNumber.java          | 43 +++++++++++++++++++
 .../maths/StrobogrammaticNumberTest.java      | 19 ++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/maths/StrobogrammaticNumber.java
 create mode 100644 src/test/java/com/thealgorithms/maths/StrobogrammaticNumberTest.java

diff --git a/src/main/java/com/thealgorithms/maths/StrobogrammaticNumber.java b/src/main/java/com/thealgorithms/maths/StrobogrammaticNumber.java
new file mode 100644
index 000000000..bcd9a8467
--- /dev/null
+++ b/src/main/java/com/thealgorithms/maths/StrobogrammaticNumber.java
@@ -0,0 +1,43 @@
+package com.thealgorithms.maths;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A strobogrammatic number is a number that remains the same when rotated 180 degrees.
+ * In other words, the number looks the same when rotated upside down.
+ * Examples of strobogrammatic numbers are "69", "88", "818", and "101".
+ * Numbers like "609" or "120" are not strobogrammatic because they do not look the same when rotated.
+ */
+public class StrobogrammaticNumber {
+    /**
+     * Check if a number is strobogrammatic
+     * @param number the number to be checked
+     * @return true if the number is strobogrammatic, false otherwise
+     */
+    public boolean isStrobogrammatic(String number) {
+        Map<Character, Character> strobogrammaticMap = new HashMap<>();
+        strobogrammaticMap.put('0', '0');
+        strobogrammaticMap.put('1', '1');
+        strobogrammaticMap.put('6', '9');
+        strobogrammaticMap.put('8', '8');
+        strobogrammaticMap.put('9', '6');
+
+        int left = 0;
+        int right = number.length() - 1;
+
+        while (left <= right) {
+            char leftChar = number.charAt(left);
+            char rightChar = number.charAt(right);
+
+            if (!strobogrammaticMap.containsKey(leftChar) || strobogrammaticMap.get(leftChar) != rightChar) {
+                return false;
+            }
+
+            left++;
+            right--;
+        }
+
+        return true;
+    }
+}
diff --git a/src/test/java/com/thealgorithms/maths/StrobogrammaticNumberTest.java b/src/test/java/com/thealgorithms/maths/StrobogrammaticNumberTest.java
new file mode 100644
index 000000000..2269291e0
--- /dev/null
+++ b/src/test/java/com/thealgorithms/maths/StrobogrammaticNumberTest.java
@@ -0,0 +1,19 @@
+package com.thealgorithms.maths;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class StrobogrammaticNumberTest {
+
+    @Test
+    void testIsStrobogrammatic() {
+        StrobogrammaticNumber strobogrammaticNumber = new StrobogrammaticNumber();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("69")).isTrue();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("88")).isTrue();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("818")).isTrue();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("101")).isTrue();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("609")).isTrue();
+        assertThat(strobogrammaticNumber.isStrobogrammatic("120")).isFalse();
+    }
+}