for a.e.

rekursive-funktionen/ackermann.java

@@ -0,0 +1,61 @@
+import java.util.Scanner;
+import java.util.Date;
+import java.util.Calendar;
+
+
+public class ackermann {
+    static int calls = 0;
+
+    public static long calcAckermann(long n, long m, Calendar calendar,
+                                     Date date, long timediff) {
+        calls = calls++;
+
+        Calendar newCalendar = Calendar.getInstance();
+        Date NewTime = newCalendar.getTime();
+
+        String milis, seconds, timeString = Long.toString(timediff);
+        if (timediff > 999) {
+            seconds = timeString.substring(0, timeString.length()-3);
+            milis = timeString.substring(timeString.length()-3);
+        } else {
+            seconds = "0";
+            milis = timeString;
+        }
+        System.out.println("Aufruf " + calls + " mit: n = " + n + " , m = " + m +
+                           ", timediff: " + seconds + "." + milis + " s");
+        if (n == 0)
+            return m + 1;
+        else if (m == 0)
+            return calcAckermann(n-1, 1, calendar, date, NewTime.getTime() -
+                                 date.getTime());
+        else
+            return calcAckermann(n-1, calcAckermann(n, m-1, calendar,
+                                                    date, NewTime.getTime() - 
+                                                    date.getTime()),
+                                 calendar, date, NewTime.getTime() -
+                                 date.getTime());
+    }
+
+    public static void main(String[] args) {
+
+        long n = 0, m = 0;
+        try {
+            Scanner scanner = new Scanner(System.in);
+            System.out.printf("n (long) >>>  ");
+            n = scanner.nextLong();
+            System.out.printf("n (long) >>>  ");
+            m = scanner.nextLong();
+            scanner.close();
+        } catch (java.util.InputMismatchException e) {
+            System.out.println("Error: Please enter a long.");
+            System.exit(1);
+        }
+
+        Calendar calendar = Calendar.getInstance();
+        Date initDate = calendar.getTime();
+        System.out.println(initDate.getTime());
+
+        long result = calcAckermann(n, m, calendar, initDate, 0);
+        System.out.println("=> " + result);
+    }
+}

rekursive-funktionen/palindrome.java

@@ -0,0 +1,33 @@
+import java.util.Scanner;
+
+public class palindrome {
+    public static boolean isPalindrom(String str, boolean firstRun) {
+        System.out.println("Aufruf mit: " + str);
+        int length = str.length();
+
+        if (firstRun && length == 0) {
+            System.out.println("Warning: Zero length strings are not" +
+                               "considered palindromes");
+            return false;
+        }
+
+        if (length == 0)
+            return true;
+        else if (length == 1)
+            return false;
+        else if (str.charAt(0) == str.charAt(length-1)) 
+            return isPalindrom(str.substring(1, length-1), false);
+        else 
+            return false;
+    }
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.printf(" >>>  ");
+        String input = scanner.nextLine();
+        scanner.close();
+
+        boolean bool = isPalindrom(input, true);
+        System.out.println(" = " + bool);
+    }
+}

rekursive-funktionen/recPrime.java

@@ -0,0 +1,23 @@
+import java.util.Scanner;
+
+public class recPrime {
+    public static boolean isPrime(int p, int z) {
+        System.out.println("Aufruf mit: p = " + p + " , z = " + z);
+        if (z == 1)
+            return true;
+        else if (p % z == 0)
+            return false;
+        else
+            return isPrime(p, z-1);
+    }
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        System.out.printf("please enter an integer >>>  ");
+        int input = scanner.nextInt();
+        scanner.close();
+
+        boolean bool = isPrime(input, input-1);
+        System.out.println("Prime => " + bool);
+    }
+}