/*
https://leetcode.com/problems/zigzag-conversion/
Runtime: 3 ms, faster than 95.99% of Java online submissions for ZigZag Conversion.
Memory Usage: 37.1 MB, less than 100.00% of Java online submissions for ZigZag Conversion.
*/
class Solution {
    public String convert(String s, int numRows) {
        final int sl=s.length();
        if (numRows < 2 || sl <= numRows) {
            return s;
        }

        final int b = (numRows - 1) * 2;
        int j = 0, o1 = 0, o2 = 0;
        StringBuilder zz = new StringBuilder(sl);
        for (int i=0; i<numRows; ++i) {
            j = i;
            o1 = 2*i;
            o2 = b-o1;
            zz.append(s.charAt(j));
            while(j<sl) {
                if (o2 > 0) {
                    j += o2;
                    if (j<sl) {
                        zz.append(s.charAt(j));
                    }
                }
                if (o1 > 0) {
                    j += o1;
                    if (j<sl) {
                        zz.append(s.charAt(j));
                    }
                }
            }
        }
        return zz.toString();
    }
}