public static boolean check ( String txt ) {
  HashSet < Integer > set = new HashSet < Integer > ( ) ;
  for ( int i = 0 ;
  i < txt . length ( ) ;
  i ++ ) set . add ( ( int ) txt . charAt ( i ) ) ;
  if ( set . size ( ) > 2 ) return false ;
  else return true ;
}

public static boolean check ( String txt ) { HashSet < Integer > set = new HashSet < Integer > ( ) ; for ( int i = 0 ; i < txt . length ( ) ; i ++ ) set . add ( ( int ) txt . charAt ( i ) ) ; if ( set . size ( ) > 2 ) return false ; else return true ; }
(method_declaration (modifiers) type: (boolean_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier))) body: (block (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments (type_identifier))) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))) update: (update_expression (identifier)) body: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (cast_expression type: (integral_type) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))))))) (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (decimal_integer_literal))) consequence: (return_statement (false)) alternative: (return_statement (true)))))