构建一个班级信息链表类，学生信息包括：学号（ID）、姓名（Name）、出生年月（Birth）、性别(Sex)和某门功课成绩（Score）。类的成员函数只需要满足本题要求即可，学生人数由用户决定。为避免大量输入工作，建议学生信息从文件读入，文件格式可自行设定并描述清楚。实现：（1）按成绩降序排列，（2）汇总各分数段人数。分数段划分区间为[90,100]，[80,90)，[70,80), [60,70), [0,60)，(3)列出最高分和最低分的同学信息。（注：不允许使用STL，否则不计成绩）

以下是一个班级信息链表类的示例代码，满足题目要求：

#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>

using namespace std;

// 学生信息结构体
struct Student {
    int ID;
    string Name;
    string Birth;
    string Sex;
    int Score;
    Student* next;
};

class StudentList {
public:
    StudentList(): head(NULL), num(0) {}
    ~StudentList() { clear(); }
    
    // 从文件中读入学生信息
    void readFromFile(const char* filename) {
        ifstream fin(filename);
        if (!fin) {
            cerr << "Failed to open file " << filename << endl;
            return;
        }
        clear();
        while (!fin.eof()) {
            Student* p = new Student;
            fin >> p->ID >> p->Name >> p->Birth >> p->Sex >> p->Score;
            addStudent(p);
        }
    }

    // 按成绩降序排列
    void sortByScore() {
        if (num <= 1) {
            return;
        }
        Student* p = head;
        while (p != NULL) {
            Student* q = p->next;
            while (q != NULL) {
                if (p->Score < q->Score) {
                    swap(p, q);
                }
                q = q->next;
            }
            p = p->next;
        }
    }

    // 汇总各分数段人数
    void countByScore() {
        int count[6] = {0};
        Student* p = head;
        while (p != NULL) {
            if (p->Score >= 90) {
                count[0]++;
            } else if (p->Score >= 80) {
                count[1]++;
            } else if (p->Score >= 70) {
                count[2]++;
            } else if (p->Score >= 60) {
                count[3]++;
            } else {
                count[4]++;
            }
            p = p->next;
        }
        count[5] = num - count[0] - count[1] - count[2] - count[3] - count[4];
        cout << "Score Summary:" << endl;
        cout << "90-100: " << count[0] << endl;
        cout << "80-90: " << count[1] << endl;
        cout << "70-80: " << count[2] << endl;
        cout << "60-70: " << count[3] << endl;
        cout << "0-60: " << count[4] << endl;
        cout << "Invalid: " << count[5] << endl;
    }

    // 列出最高分和最低分的同学信息
    void printMaxMin() {
        if (num == 0) {
            cout << "No students found" << endl;
            return;
        }
        Student* p = head;
        Student* maxStu = p;
        Student* minStu = p;
        while (p != NULL) {
            if (p->Score > maxStu->Score) {
                maxStu = p;
            }
            if (p->Score < minStu->Score) {
                minStu = p;
            }
            p = p->next;
        }
        cout << "Max Score:" << endl;
        printStudent(maxStu);
        cout << "Min Score:" << endl;
        printStudent(minStu);
    }

    // 清空链表
    void clear() {
        Student* p = head;
        while (p != NULL) {
            Student* q = p->next;
            delete p;
            p = q;
        }
        head = NULL;
        num = 0;
    }

private:
    Student* head;
    int num;

    // 添加一个学生到链表中
    void addStudent(Student* p) {
        p->next = head;
        head = p;
        num++;
    }

    // 输出一个学生的信息
    void printStudent(Student* p) {
        cout << "ID: " << p->ID << endl;
        cout << "Name: " << p->Name << endl;
        cout << "Birth: " << p->Birth << endl;
        cout << "Sex: " << p->Sex << endl;
        cout << "Score: " << p->Score << endl;
    }

    // 交换两个学生的位置
    void swap(Student*& p, Student*& q) {
        Student* temp = p;
        p = q;
        q = temp;
    }
};

int main() {
    StudentList list;
    list.readFromFile("students.txt");
    list.sortByScore();
    cout << "Sorted by score:" << endl;
    Student* p = list.head;
    while (p != NULL) {
        list.printStudent(p);
        p = p->next;
    }
    list.countByScore();
    list.printMaxMin();
    list.clear();
    return 0;
}

文件格式示例（每行代表一个学生信息）：

1 Alice 2000-01-01 F 90
2 Bob 2001-02-03 M 85
3 Charlie 2002-03-05 M 80
4 David 2003-04-07 M 95
5 Emily 2004-05-09 F 75