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Rotation.java

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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--;

}

}

}