分组，余数补在前

public static void main(String[] args) {
    int selectNumber = 2;//分组数量
    Set<SignStudentEntity> students = new HashSet<>();
    for(int non=1; non<=10; non++){
        students.add(new SignStudentEntity(non));
    }

    int size = students.size(); //容量
    int j = size / selectNumber; //取模
    int k = size % selectNumber; //取余
    int m = 1;
    int i = 1;
    for(SignStudentEntity signStudent : students){
        if(i <= j * m + k){
            signStudent.setGroupNumber(m);
        }else{
            m+=1;
            signStudent.setGroupNumber(m);
        }
        i+=1;
    }

    System.out.println(size / selectNumber);  //4
    System.out.println(size % selectNumber);  //1
    System.out.println(students);
}