public class PRGString {
    public static boolean esPrefijo(String a, String b) {
        if (a.length() == 0) { return true; }
        else if (a.length() > b.length()) { return false; }
        else if (a.charAt(0) == b.charAt(0)) {
            return esPrefijo(
                a.substring(1),
                b.substring(1) );
            }
        else { return false; }
    }

    public static boolean esSubcadena(String a, String b) {
        if (a.length() == 0) { return true; }
        else if (a.length() > b.length()) { return false; }
        else if (a.charAt(0) == b.charAt(0)) { return esPrefijo(a, b); }
        else { return esSubcadena(a, b.substring(1)); }
    }

    public static boolean esPalindromoSA(String a) {
        a = a.toLowerCase();
        if (a.length() == 0 || a.length() == 1) { return true;}
        else if (a.charAt(0) == a.charAt(a.length() - 1)) {
            return esPalindromoSA(a.substring(1, a.length() - 1)); }
        else if (a.charAt(0) != a.charAt(a.length() - 1)) {
            if (!Character.isLetter(a.charAt(0))) {
                return esPalindromoSA(a.substring(1, a.length())); }
            else if (!Character.isLetter(a.charAt(a.length() - 1))) {
                return esPalindromoSA(a.substring(0, a.length() - 1)); }
        }
        return false;
    }

    public static boolean esPalindromo(String a){
        a = a.toLowerCase();

        a = a.replace('á', 'a').replace('é', 'e').replace('í', 'i').replace('ó', 'o').replace('ú', 'u');
        if (a.length() == 0 || a.length() == 1) { return true;}
        else if (a.charAt(0) == a.charAt(a.length() - 1)) {
            return esPalindromoSA(a.substring(1, a.length() - 1)); }
        else if (a.charAt(0) != a.charAt(a.length() - 1)) {
            if (!Character.isLetter(a.charAt(0))) {
                return esPalindromoSA(a.substring(1, a.length())); }
            else if (!Character.isLetter(a.charAt(a.length() - 1))) {
                return esPalindromoSA(a.substring(0, a.length() - 1)); }
        }
        return false;
    }
}