1 string convert(string s, int nRows) { 2         string res; 3          4         if (nRows <= 1) 5             return s; 6          7         for (int r = 0; r < nRows; r++) { 8             int curr = r; 9             int prev = -1;10             bool toggle = true;11             while (curr < s.length()) {12                 if (prev != curr)13                     res += s[curr];14                 prev = curr;15                 curr += toggle ? 2 * (nRows - r - 1) : 2 * r;16                 toggle = !toggle;17             }18         }19         20         return res;21 }