From e5a929d6483ca012dda40a46a44c0a742618498f Mon Sep 17 00:00:00 2001
From: Shivam Thorat <131280083+shivamuser75@users.noreply.github.com>
Date: Tue, 1 Oct 2024 20:28:20 +0530
Subject: [PATCH] Add basic recursion algorithms

---
 .../com/thealgorithms/recursion/Factorial.java  | 11 +++++++++++
 .../com/thealgorithms/recursion/Fibonacci.java  | 11 +++++++++++
 .../thealgorithms/recursion/Permutations.java   | 17 +++++++++++++++++
 .../com/thealgorithms/recursion/Subsets.java    | 15 +++++++++++++++
 .../thealgorithms/recursion/TowerOfHanoi.java   | 14 ++++++++++++++
 5 files changed, 68 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/recursion/Factorial.java
 create mode 100644 src/main/java/com/thealgorithms/recursion/Fibonacci.java
 create mode 100644 src/main/java/com/thealgorithms/recursion/Permutations.java
 create mode 100644 src/main/java/com/thealgorithms/recursion/Subsets.java
 create mode 100644 src/main/java/com/thealgorithms/recursion/TowerOfHanoi.java

diff --git a/src/main/java/com/thealgorithms/recursion/Factorial.java b/src/main/java/com/thealgorithms/recursion/Factorial.java
new file mode 100644
index 000000000000..68269208a995
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/Factorial.java
@@ -0,0 +1,11 @@
+package com.thealgorithms.recursion;
+
+public class Factorial {
+
+    public static int factorial(int n) {
+        if (n == 0) {
+            return 1;
+        }
+        return n * factorial(n - 1);
+    }
+}
diff --git a/src/main/java/com/thealgorithms/recursion/Fibonacci.java b/src/main/java/com/thealgorithms/recursion/Fibonacci.java
new file mode 100644
index 000000000000..c800387c56be
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/Fibonacci.java
@@ -0,0 +1,11 @@
+package com.thealgorithms.recursion;
+
+public class Fibonacci {
+
+    public static int fibonacci(int n) {
+        if (n <= 1) {
+            return n;
+        }
+        return fibonacci(n - 1) + fibonacci(n - 2);
+    }
+}
diff --git a/src/main/java/com/thealgorithms/recursion/Permutations.java b/src/main/java/com/thealgorithms/recursion/Permutations.java
new file mode 100644
index 000000000000..80731f32a1e9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/Permutations.java
@@ -0,0 +1,17 @@
+package com.thealgorithms.recursion;
+
+import java.util.ArrayList;
+
+public class Permutations {
+
+    public static void permute(String str, String prefix, ArrayList<String> result) {
+        if (str.length() == 0) {
+            result.add(prefix);
+        } else {
+            for (int i = 0; i < str.length(); i++) {
+                String rem = str.substring(0, i) + str.substring(i + 1);
+                permute(rem, prefix + str.charAt(i), result);
+            }
+        }
+    }
+}
diff --git a/src/main/java/com/thealgorithms/recursion/Subsets.java b/src/main/java/com/thealgorithms/recursion/Subsets.java
new file mode 100644
index 000000000000..188cf585c045
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/Subsets.java
@@ -0,0 +1,15 @@
+package com.thealgorithms.recursion;
+
+import java.util.ArrayList;
+
+public class Subsets {
+
+    public static void subset(String prefix, String str, ArrayList<String> result) {
+        if (str.length() == 0) {
+            result.add(prefix);
+            return;
+        }
+        subset(prefix + str.charAt(0), str.substring(1), result);
+        subset(prefix, str.substring(1), result);
+    }
+}
diff --git a/src/main/java/com/thealgorithms/recursion/TowerOfHanoi.java b/src/main/java/com/thealgorithms/recursion/TowerOfHanoi.java
new file mode 100644
index 000000000000..9db2a10fc8b9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/recursion/TowerOfHanoi.java
@@ -0,0 +1,14 @@
+package com.thealgorithms.recursion;
+
+public class TowerOfHanoi {
+
+    public static void solve(int n, char from, char to, char aux) {
+        if (n == 1) {
+            System.out.println("Move disk 1 from rod " + from + " to rod " + to);
+            return;
+        }
+        solve(n - 1, from, aux, to);
+        System.out.println("Move disk " + n + " from rod " + from + " to rod " + to);
+        solve(n - 1, aux, to, from);
+    }
+}