* rename file

* create strings directory
* fix docs
* add test

Maths/Armstrong.java

@@ -1,4 +1,4 @@
-package Others;
+package strings;
 
 /**
  * An Armstrong number is equal to the sum of the cubes of its digits.

Others/Abecedarian.java

@@ -1,24 +0,0 @@
-package Others;
-
-/**
- * An Abecadrian is a word where each letter is in alphabetical order
- *
- * @author Oskar Enmalm
- */
-class Abecedarian {
-
-    public static boolean isAbecedarian(String s) {
-        int index = s.length() - 1;
-
-        for (int i = 0; i < index; i++) {
-
-            if (s.charAt(i) <= s.charAt(i + 1)) {
-            } //Need to check if each letter for the whole word is less than the one before it
-
-            else {
-                return false;
-            }
-        }
-        return true;
-    }
-}

Others/Palindrome.java

@@ -1,50 +0,0 @@
-package Others;
-
-class Palindrome {
-
-    private String reverseString(String x) { // *helper method
-        StringBuilder output = new StringBuilder(x);
-        return output.reverse().toString();
-    }
-
-    public boolean FirstWay(String x) { // *palindrome method, returns true if palindrome
-        if (x == null || x.length() <= 1)
-            return true;
-        return x.equalsIgnoreCase(reverseString(x));
-    }
-
-    public boolean SecondWay(String x) {
-        if (x.length() == 0 || x.length() == 1)
-            return true;
-
-        if (x.charAt(0) != x.charAt(x.length() - 1))
-            return false;
-
-        return SecondWay(x.substring(1, x.length() - 1));
-    }
-
-    /**
-     * This method ignores all non-alphanumeric characters and case runs in O(n)
-     * where n is the length of s
-     * 
-     * @param s String to check
-     * @return true if s is palindrome else false
-     */
-    public boolean isPalindrome(String s) {
-        s = s.toLowerCase().trim();
-        StringBuilder sb = new StringBuilder();
-        for (char c : s.toCharArray()) {
-            if (Character.isLetter(c) || Character.isDigit(c))
-                sb.append(c);
-        }
-        s = sb.toString();
-        int start = 0;
-        int end = s.length() - 1;
-        while (start <= end) {
-            if (s.charAt(start++) != s.charAt(end--))
-                return false;
-
-        }
-        return true;
-    }
-}

Others/ReverseString.java

@@ -1,46 +0,0 @@
-package Others;
-
-import java.io.BufferedReader;
-import java.io.IOException;
-import java.io.InputStreamReader;
-
-/**
- * This method produces a reversed version of a string
- *
- * @author Unknown
- */
-public class ReverseString {
-
-    /**
-     * This method reverses the string str and returns it
-     *
-     * @param str String to be reversed
-     * @return Reversed string
-     */
-    public static String reverse(String str) {
-        if (str == null || str.isEmpty()) return str;
-
-        char[] arr = str.toCharArray();
-        for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
-            char temp = arr[i];
-            arr[i] = arr[j];
-            arr[j] = temp;
-        }
-        return new String(arr);
-    }
-
-    /**
-     * Main Method
-     *
-     * @param args Command line arguments
-     * @throws IOException Exception thrown because of BufferedReader
-     */
-    public static void main(String[] args) throws IOException {
-        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
-        System.out.println("Enter the string");
-        String srr = br.readLine();
-        System.out.println("Reverse=" + reverse(srr));
-        br.close();
-    }
-}
-		

strings/Alphabetical.java

@@ -0,0 +1,35 @@
+package strings;
+
+/**
+ * <p>
+ * Alphabetical order is a system whereby character strings are placed in order
+ * based on the position of the characters in the conventional ordering of an alphabet.
+ * </p>
+ * Wikipedia: https://en.wikipedia.org/wiki/Alphabetical_order
+ */
+class Alphabetical {
+
+    public static void main(String[] args) {
+        assert !isAlphabetical("123abc");
+        assert isAlphabetical("aBC");
+        assert isAlphabetical("abc");
+        assert !isAlphabetical("xyzabc");
+        assert isAlphabetical("abcxyz");
+    }
+
+    /**
+     * Check if a string is alphabetical order or not
+     *
+     * @param s a string
+     * @return {@code true} if given string is alphabetical order, otherwise {@code false}
+     */
+    public static boolean isAlphabetical(String s) {
+        s = s.toLowerCase();
+        for (int i = 0; i < s.length() - 1; ++i) {
+            if (!Character.isLetter(s.charAt(i)) || !(s.charAt(i) <= s.charAt(i + 1))) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

strings/Palindrome.java

@@ -0,0 +1,68 @@
+package strings;
+
+/**
+ * Wikipedia: https://en.wikipedia.org/wiki/Palindrome
+ */
+class Palindrome {
+
+    /**
+     * Driver Code
+     */
+    public static void main(String[] args) {
+        String[] palindromes = {null, "", "aba", "123321"};
+        for (String s : palindromes) {
+            assert isPalindrome(s) && isPalindromeRecursion(s) && isPalindrome1(s);
+        }
+
+        String[] notPalindromes = {"abb", "abc", "abc123"};
+        for (String s : notPalindromes) {
+            assert !isPalindrome(s) && !isPalindromeRecursion(s) && !isPalindrome1(s);
+        }
+    }
+
+    /**
+     * Check if a string is palindrome string or not
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise {@code false}
+     */
+    public static boolean isPalindrome(String s) {
+        return (s == null || s.length() <= 1) || s.equals(new StringBuilder(s).reverse().toString());
+    }
+
+    /**
+     * Check if a string is palindrome string or not using recursion
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise {@code false}
+     */
+    public static boolean isPalindromeRecursion(String s) {
+        if (s == null || s.length() <= 1) {
+            return true;
+        }
+
+        if (s.charAt(0) != s.charAt(s.length() - 1)) {
+            return false;
+        }
+
+        return isPalindrome(s.substring(1, s.length() - 1));
+    }
+
+    /**
+     * Check if a string is palindrome string or not another way
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise {@code false}
+     */
+    public static boolean isPalindrome1(String s) {
+        if (s == null || s.length() <= 1) {
+            return true;
+        }
+        for (int i = 0, j = s.length() - 1; i < j; ++i, --j) {
+            if (s.charAt(i) != s.charAt(j)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

strings/ReverseString.java

@@ -0,0 +1,44 @@
+package strings;
+
+/**
+ * Reverse String using different version
+ */
+public class ReverseString {
+
+    public static void main(String[] args) {
+        assert reverse("abc123").equals("321cba");
+        assert reverse2("abc123").equals("321cba");
+    }
+
+    /**
+     * easiest way to reverses the string str and returns it
+     *
+     * @param str string to be reversed
+     * @return reversed string
+     */
+    public static String reverse(String str) {
+        return new StringBuilder(str).reverse().toString();
+    }
+
+    /**
+     * second way to reverses the string str and returns it
+     *
+     * @param str string to be reversed
+     * @return reversed string
+     */
+    public static String reverse2(String str) {
+
+        if (str == null || str.isEmpty()) {
+            return str;
+        }
+        
+        char[] value = str.toCharArray();
+        for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
+            char temp = value[i];
+            value[i] = value[j];
+            value[j] = temp;
+        }
+        return new String(value);
+    }
+
+}