static int minSwaps ( String s1 , String s2 ) {
  int c0 = 0 , c1 = 0 ;
  for ( int i = 0 ;
  i < s1 . length ( ) ;
  i ++ ) {
    if ( s1 . charAt ( i ) == '0' && s2 . charAt ( i ) == '1' ) {
      c0 ++ ;
    }
    else if ( s1 . charAt ( i ) == '1' && s2 . charAt ( i ) == '0' ) {
      c1 ++ ;
    }
  }
  int ans = c0 / 2 + c1 / 2 ;
  if ( c0 % 2 == 0 && c1 % 2 == 0 ) {
    return ans ;
  }
  else if ( ( c0 + c1 ) % 2 == 0 ) {
    return ans + 2 ;
  }
  else {
    return - 1 ;
  }
}

static int minSwaps ( String s1 , String s2 ) { int c0 = 0 , c1 = 0 ; for ( int i = 0 ; i < s1 . length ( ) ; i ++ ) { if ( s1 . charAt ( i ) == '0' && s2 . charAt ( i ) == '1' ) { c0 ++ ; } else if ( s1 . charAt ( i ) == '1' && s2 . charAt ( i ) == '0' ) { c1 ++ ; } } int ans = c0 / 2 + c1 / 2 ; if ( c0 % 2 == 0 && c1 % 2 == 0 ) { return ans ; } else if ( ( c0 + c1 ) % 2 == 0 ) { return ans + 2 ; } else { return - 1 ; } }
(method_declaration (modifiers) type: (integral_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier)) (formal_parameter type: (type_identifier) name: (identifier))) body: (block (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal)) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (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: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (update_expression (identifier)))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)) right: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))) right: (character_literal)))) consequence: (block (expression_statement (update_expression (identifier)))))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (binary_expression left: (identifier) right: (decimal_integer_literal))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)) right: (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal)))) consequence: (block (return_statement (identifier))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (identifier))) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (return_statement (binary_expression left: (identifier) right: (decimal_integer_literal)))) alternative: (block (return_statement (unary_expression operand: (decimal_integer_literal))))))))