[LeetCode] ZigZag Conversion

class Solution {public:    string convert(string s, int nRows) {        string res[nRows];        string ss = "";        int length = s.length();        int i = 0;        while(i < length){            for(int r = 0; (r < nRows) && (i < length); ++ r)                res[r] += s[i ++];            for(int rr = nRows - 2; (rr > 0) && (i < length);rr --)                res[rr] += s[i ++];        }        for(int r = 0;r < nRows; ++ r)             ss += res[r];        return ss;    }};