Merge pull request #1449 from shellhub/dev

Added rotation string

DIRECTORY.md

@@ -241,4 +241,5 @@
   * [Palindrome](https://github.com/TheAlgorithms/Java/blob/master/strings/Palindrome.java)
   * [Pangram](https://github.com/TheAlgorithms/Java/blob/master/strings/Pangram.java)
   * [ReverseString](https://github.com/TheAlgorithms/Java/blob/master/strings/ReverseString.java)
+  * [Rotation](https://github.com/TheAlgorithms/Java/blob/master/strings/Rotation.java)
   * [Upper](https://github.com/TheAlgorithms/Java/blob/master/strings/Upper.java)

strings/Rotation.java

@@ -0,0 +1,64 @@
+package strings;
+
+
+/**
+ * Given a string, moving several characters
+ * in front of the string to the end of the string.
+ * For example, move the two characters'a' and 'b' in
+ * front of the string "abcdef" to the end of the string,
+ * so that the original string becomes the string "cdefab"
+ */
+public class Rotation {
+    public static void main(String[] args) {
+        assert rotation("abcdef", 2).equals("cdefab");
+
+        char[] values = "abcdef".toCharArray();
+        rotation(values, 2);
+        assert new String(values).equals("cdefab");
+    }
+
+    /**
+     * Move {@code n} characters in front of given string to the end of string
+     * time complexity: O(n)
+     * space complexity: O(n)
+     *
+     * @param s given string
+     * @param n the total characters to be moved
+     * @return string after rotation
+     */
+    public static String rotation(String s, int n) {
+        return s.substring(n) + s.substring(0, n);
+    }
+
+    /**
+     * Move {@code n} characters in front of given character array to the end of array
+     * time complexity: O(n)
+     * space complexity: O(1)
+     *
+     * @param values given character array
+     * @param n      the total characters to be moved
+     */
+    public static void rotation(char[] values, int n) {
+        reverse(values, 0, n - 1);
+        reverse(values, n, values.length - 1);
+        reverse(values, 0, values.length - 1);
+    }
+
+    /**
+     * Reverse character array
+     *
+     * @param values character array
+     * @param from   begin index of given array
+     * @param to     end index of given array
+     */
+    public static void reverse(char[] values, int from, int to) {
+        while (from < to) {
+            char temp = values[from];
+            values[from] = values[to];
+            values[to] = temp;
+            from++;
+            to--;
+        }
+    }
+
+}