Rotate String

Problem:

Given a string and an offset, rotate string by offset. (rotate from left to right)

Have you met this question in a real interview?

Yes

Example

Given "abcdefg".

offset=0 => "abcdefg"
offset=1 => "gabcdef"
offset=2 => "fgabcde"
offset=3 => "efgabcd"

Analysis:
感觉这道题应该归为medium, 自己想肯定想不出来。
Take offset  = 2 as an example. Reverse abcde first, then reverse fg, reverse the whole string at last.
Step 1： edcbafg
Step 2:    edcbagf
Step 3:    fgabcde

Solution：
Offset > str.length has take into consideration. Pre process offset by offset%str.length.

public class Solution {
    /**
     * @param str: An array of char
     * @param offset: An integer
     * @return: nothing
     */
    public void rotateString(char[] str, int offset) {
        // write your code here
        if (str == null || str.length == 0) return;
        offset = offset % str.length;
        reverse(str, 0, str.length - offset - 1);
        reverse(str, str.length - offset, str.length - 1);
        reverse(str, 0, str.length - 1);
    }

    private void reverse(char[] str, int start, int end) {
        while (start < end) {
            char temp = str[start];
            str[start] = str[end];
            str[end] = temp;
            start++;
            end--;
        }
    }
}