LintCode: Rotate String

C++,

time: O(n)

space:O(n)

class Solution {
public:
    /**
     * @param str: a string
     * @param offset: an integer
     * @return: nothing
     */
    void rotateString(string &str, int offset) {
        // wirte your code here
        // empty string->return
        if ("" == str) {
            return;
        }
        // offset is 0, return
        int size = str.size();
        offset = offset%size;
        if (0 == offset) {
            return;
        }
        // tmp = str+str->substr
        string tmp(str);
        tmp.reserve(size<<1);
        tmp.insert(tmp.end(), str.begin(), str.end());
        str = tmp.substr(size-offset, size);
    }
};

 C++,

time:O(n)

space:O(1)

class Solution {
public:
    /**
     * @param str: a string
     * @param offset: an integer
     * @return: nothing
     */
    void rotateString(string &str, int offset) {
        // wirte your code here
        // empty string->return
        if ("" == str) {
            return;
        }
        // offset is 0, return
        int size = str.size();
        offset = offset%size;
        if (0 == offset) {
            return;
        }
        // 3-steps reverse
        reverse(str, 0, size-offset-1);
        reverse(str, size-offset, size-1);
        reverse(str, 0, size-1);
    }
    void reverse(string &str, int from, int to) {
        char tmp;
        while( from<to ) {
            tmp = str[from];
            str[from] = str[to];
            str[to] = tmp;
            from++;
            to--;
        }
    } 
};