[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 = 0;
        
        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 <= 0)    return ;
        if( offset > len )  offset %= len;
        
        // Reverse the first section.
        reverseString(str, 0, len-offset-1);
        // Reverse the second section.
        reverseString(str, len-offset, len-1);
        // Reverse the entire section.
        reverseString(str, 0, len-1);
        
        return ;
    }