Rotate String

Source

• lintcode: Rotate String

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

Example
Given "abcdefg".

offset=0 => "abcdefg"
offset=1 => "gabcdef"
offset=2 => "fgabcde"
offset=3 => "efgabcd"
Challenge
Rotate in-place with O(1) extra memory.

Java

public class Solution {
    /**
     * @param str: an array of char
     * @param offset: an integer
     * @return: nothing
     */
    public void rotateString(char[] str, int offset) {
        if(str==null || str.length==0) return;
        int len = str.length;
        offset %= len;

        reverse(str, 0, len-1);
        reverse(str, 0, offset-1);
        reverse(str, offset, len-1);
    }

    public void reverse(char[] str, int left, int right){
        while(left<right){
            char tmp = str[left];
            str[left]=str[right];
            str[right]=tmp;
            left++;
            right--;
        }
    }
}