package com.company;

public class Main {

    public static void main(String[] args) {
        System.out.println(revAndDouble("rivka"));
        System.out.println(makeWeirdString("steve gregg"));
        System.out.println(countPairs("proof school"));
    }
    private static String revAndDouble(String st)
    {
        if (st.length() == 0){
            return "";
        }
        return revAndDouble(st.substring(1)) + st.charAt(0) + st.charAt(0);
    }
    private static String makeWeirdString(String st)
    {
        if (st.length() == 0){
            return "";
        }
        if (st.charAt(0) == 'k') {
            return 'g' + makeWeirdString(st.substring(1));
        }
        if (st.charAt(0) == 'e') {
            return makeWeirdString(st.substring(1));
        }
        else{
            return st.charAt(0) + makeWeirdString(st.substring(1));}
    }
    private static int countPairs(String st)
    {
        if (st.length() <= 1){
            return 0;
        }
        if (st.charAt(0) == st.charAt(1)) {
            return 1 + countPairs(st.substring(1));
        }
        else{
            return countPairs(st.substring(1));
        }
    }
}