Zigzag String

• Time : $O(|A|)$
• Space : $O(|A|)$

string Solution::convert(string A, int B) {
    if(B == 1) return A;
    int left = (B - 1) * 2, right = 0;
    string res = "";
    for(int i = 0; i < B; i++,left -= 2, right += 2) {
        bool fl = true;
        int j = i;
        while(j < A.length()) {
            res.push_back(A[j]);
            if(left == 0 or right == 0) j += (B - 1) * 2;
            else if(fl) j += left;
            else j += right;
            fl = !fl;
        }
    }
    return res;
}