LeetCode – Refresh – ZigZag Conversion

class Solution {
public:
    string convert(string s, int nRows) {
        if (nRows < 2) return s;
        int len = s.size(), size = 2*nRows - 2;
        string result;
        for (int i = 0; i < nRows; i++) {
            for (int j = i; j < len; j += size) {
                result += s[j];
                if (i != 0 && i != nRows-1 && (j + size - 2*i) < len) {
                    result += s[j+size-2*i];
                }
            }
        }
        return result;
    }
};