From 81ba9eb66f8284d8760012973f84cdbe617ceb94 Mon Sep 17 00:00:00 2001
From: pants <niklasjo2004@gmail.com>
Date: Mon, 21 Sep 2026 14:16:34 -0700
Subject: init

---
 in_class/cse123-inclass9/IsPalindromeArray.java  | 25 ++++++++++++++++
 in_class/cse123-inclass9/IsPalindromeString.java | 19 ++++++++++++
 in_class/cse123-inclass9/RecursiveMystery.java   | 38 ++++++++++++++++++++++++
 in_class/cse123-inclass9/ReverseString.java      | 22 ++++++++++++++
 4 files changed, 104 insertions(+)
 create mode 100644 in_class/cse123-inclass9/IsPalindromeArray.java
 create mode 100644 in_class/cse123-inclass9/IsPalindromeString.java
 create mode 100644 in_class/cse123-inclass9/RecursiveMystery.java
 create mode 100644 in_class/cse123-inclass9/ReverseString.java

(limited to 'in_class/cse123-inclass9')

diff --git a/in_class/cse123-inclass9/IsPalindromeArray.java b/in_class/cse123-inclass9/IsPalindromeArray.java
new file mode 100644
index 0000000..109194d
--- /dev/null
+++ b/in_class/cse123-inclass9/IsPalindromeArray.java
@@ -0,0 +1,25 @@
+public class IsPalindromeArray {
+    public static void main(String[] args) {
+        System.out.println(isPalindrome(new int[] { 1, 2, 3, 4, 5, 4, 3, 2, 1 }));
+        System.out.println(isPalindrome(new int[] { 10, 20, 20, 10 }));
+        System.out.println(isPalindrome(new int[] { 1 }));
+        System.out.println(isPalindrome(new int[] {}));
+        System.out.println(isPalindrome(new int[] { 1, 2, 3, 4, 5 }));
+        System.out.println(isPalindrome(new int[] { 1, 2, 5, 3 }));
+        System.out.println(isPalindrome(new int[] { 10, 20, 30, 10 }));
+    }
+
+    public static boolean isPalindrome(int[] array) {
+        return isPalindrome(array, 0, array.length - 1);
+    }
+
+    private static boolean isPalindrome(int[] array, int lower, int upper) {
+        if (upper - lower < 1) {
+            return true;
+        } else if (array[lower] != array[upper]) {
+            return false;
+        } else {
+            return isPalindrome(array, lower+1,upper-1);
+        }
+    }
+}
diff --git a/in_class/cse123-inclass9/IsPalindromeString.java b/in_class/cse123-inclass9/IsPalindromeString.java
new file mode 100644
index 0000000..c8bf278
--- /dev/null
+++ b/in_class/cse123-inclass9/IsPalindromeString.java
@@ -0,0 +1,19 @@
+public class IsPalindromeString {
+    public static void main(String[] args) {
+        System.out.println(isPalindrome("racecar"));
+        System.out.println(isPalindrome("tacocat"));
+        System.out.println(isPalindrome("ABBA"));
+        System.out.println(isPalindrome("x"));
+        System.out.println(isPalindrome(""));
+        System.out.println(isPalindrome("banana"));
+        System.out.println(isPalindrome("abcbba"));
+        System.out.println(isPalindrome("bramb"));
+    }
+
+    public static boolean isPalindrome(String s) {
+        if (s.length() <= 1 || s.equals(ReverseString.reverse(s))) {
+            return true;
+        }
+        return false;
+    }
+}
diff --git a/in_class/cse123-inclass9/RecursiveMystery.java b/in_class/cse123-inclass9/RecursiveMystery.java
new file mode 100644
index 0000000..c4f9806
--- /dev/null
+++ b/in_class/cse123-inclass9/RecursiveMystery.java
@@ -0,0 +1,38 @@
+public class RecursiveMystery {
+    public static void main(String[] args) {
+        // mystery1(3);
+        // mystery2(4);
+        mystery3("taco");
+    }
+
+    public static void mystery1(int n) {
+        if (n <= 1) {
+            System.out.print(n);
+        } else {
+            mystery1(n / 2);
+            System.out.print(", " + n);
+        }
+    }
+
+    public static void mystery2(int n) {
+        if (n <= 0) {
+            System.out.print("*");
+        } else if (n % 2 == 0) {
+            System.out.print("(");
+            mystery2(n - 1);
+            System.out.print(")");
+        } else {
+            System.out.print("[");
+            mystery2(n - 1);
+            System.out.print("]");
+        }
+    }
+
+    public static void mystery3(String str) {
+        if (!str.isEmpty()) {
+            System.out.print(str.charAt(0));
+            mystery3(str.substring(1));
+            System.out.print(str.charAt(0));
+        }
+    }
+}
diff --git a/in_class/cse123-inclass9/ReverseString.java b/in_class/cse123-inclass9/ReverseString.java
new file mode 100644
index 0000000..f2a5858
--- /dev/null
+++ b/in_class/cse123-inclass9/ReverseString.java
@@ -0,0 +1,22 @@
+public class ReverseString {
+    public static void main(String[] args){
+        System.out.println(reverse("Hello"));
+        System.out.println(reverse("nathan"));
+        System.out.println(reverse("racecar"));
+        System.out.println(reverse("taco"));
+        System.out.println(reverse("ABBA"));
+        System.out.println(reverse(""));
+        System.out.println(reverse("a"));
+    }
+
+    public static String reverse(String str){
+        if (str.isEmpty()) {
+            return "";
+        } else if (str.length() == 1) {
+            return str;
+        }
+
+        String backwards = reverse(str.substring(1)) + str.charAt(0);
+        return backwards;
+    }
+}
-- 
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