public static boolean isValidateString(String s){
        int n = s.length(); 
        for(int i = 1; i < n; i++){
            char current = s.charAt(i);
            if(current == s.charAt(i-1))
                return false;    
            }
        return true; 
       }
			 
			 public static int alternate(String s) {
        int n = s.length();
        Set<String> set = new HashSet<String>( Arrays.asList(s.split("") )  );
        for(int i = 1; i < n; i++){
            char current = s.charAt(i);
            if(current == s.charAt(i-1)){
                set.remove(String.valueOf(current) );
                }
            }
        int m = set.size();
        String[]elements = set.toArray(new String[m]);
        int maxLen = 0;
        
        for(int i = 0; i < m-1; i++)
            for(int j = i+1; j < m; j++){
                char c1 = elements[i].charAt(0);
                char c2 = elements[j].charAt(0);
                String result = "";
                for(int k = 0; k < n; k++){
                    char curr = s.charAt(k);
                    if(curr == c1 || curr == c2)
                      result += curr;
                    }
                if(isValidateString(result))
                    maxLen = Math.max(maxLen, result.length());
                }
        return maxLen;

        }