public static String twoStrings(String s1, String s2) {
    boolean[] s1_array = new boolean[26];
    int base = (int)'a';
    
    for (int i = 0 ; i < s1.length() ; i++){
        int position = (int)s1.charAt(i) - base;
        
        s1_array[position] = true;
    }
    
    for (int i = 0 ; i < s2.length() ; i++){
        int position = (int)s2.charAt(i) - base;
        
        if (s1_array[position] == true) return "YES";
    }
    
    return "NO";
    }