[Algorithm] 8. Rotate String

Description

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.

Solution

     /**
      * @param str: An array of char
      * @param offset: An integer
      * @return: nothing
      */
     void reverseString(string &str, int start, int end)
     {
         int swap = ;

         while(start < end){
             // Exchange the element between the start and the end.
             swap = str[start];
             str[start] = str[end];
             str[end] = swap;

             // Move to the next index.
             start++; end--;
         }

         return ;
     }

     void rotateString(string &str, int offset) {
         // Get the length of the string.
         int len = str.length();
         if( !len || offset <= )    return ;
         if( offset > len )  offset %= len;

         // Reverse the first section.
         reverseString(str, , len-offset-);
         // Reverse the second section.
         reverseString(str, len-offset, len-);
         // Reverse the entire section.
         reverseString(str, , len-);

         return ;
     }