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--;
 }
 }

}