OneEditAppart.java

public static boolean oneEditAppart(String a, String b) {
    int edits = 0;
    if (a == null || b == null || Math.abs(a.length() - b.length()) > 1) { // Strings more than 1 in size difference
        return false;
    } else if (a.length() == b.length()) { // Strings same size, check for 0 or >1 replacements
        for (int i = 0; i < a.length(); i++) {
            if (a.charAt(i) != b.charAt(i)) {
                if (++edits > 1) return false;
            }
        }
        if (edits == 0) return false;
    } else { // if off by one, we can have an insertion or deletion. Check there is only 1
        String large = a.length() > b.length() ? a : b;
        String small = a.length() < b.length() ? a : b;

        int i = 0;
        while (i < small.length()) {
            if (small.charAt(i) != large.charAt(i + edits)) {
                if (++edits > 1)
                    return false;
            } else {
                i++;
            }
        }
    }
    return true;
}