public static String caesarCipher(String s, int k) {
    // Write your code here
        StringBuilder sb = new StringBuilder(s);
        for(int i=0;i<sb.length();i++) {
            int curr = sb.charAt(i);
            if(curr >= 65 && curr <=90) {
                int mod = ((curr % 64) + k) % 26;
                if(mod==0) mod = 26; // for Z
                sb.setCharAt(i, (char) (64+mod));
            } else if(curr >= 97 && curr <=122) {
                int mod = ((curr % 96) + k) % 26;
                if(mod==0) mod = 26;  //for z
                System.out.println("i: "+i+", mod: "+mod);
                sb.setCharAt(i, (char) (96+mod));
            }
        }
        return new String(sb);
    }