int a = sc.nextInt();
String x = sc.nextLine();

此时x会读到换行符，结束读取，所以x是换行符
要解决此问题
（1）将换行符读取掉

int a = sc.nextInt();
sc.nextLine();
String x = sc.nextLine();

（2）再创建一个Scanner对象

Scanner sc1 = new Scanner(System.in);
double k = sc.nextDouble();
Scanner sc2 = new Scanner(System.in);
String a = sc.nextLine();