6-Zigzag-Conversion.java

//We check whether we are at the diagonal or not using a boolean and increment the pointer accordingly.

class Solution {

    public String convert(String s, int row) {
        if (row == 1) return s;
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < row; i++) {
            int j = i;
            if (i == 0 || i == row - 1) {
                while (j < s.length()) {
                    sb.append(s.charAt(j));
                    j += 2 * (row - 1);
                }
            } else {
                boolean diagonal = false;
                while (j < s.length()) {
                    if (!diagonal) {
                        sb.append(s.charAt(j));
                        j += 2 * (row - i - 1);
                        diagonal = true;
                    } else {
                        sb.append(s.charAt(j));
                        j += 2 * i;
                        diagonal = false;
                    }
                }
            }
        }
        return sb.toString();
    }
}