JavaAlgorithms/Strings/Rotation.java

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--;
    }
  }
}