a1047 student list for course

Zhejiang University has 40,000 students and provides 2,500 courses. Now given the registered course list of each student, you are supposed to output the student name lists of all the courses.

Each input file contains one test case. For each case, the first line contains 2 numbers: N (≤40,000), the total number of students, and K (≤2,500), the total number of courses. Then N lines follow, each contains a student’s name (3 capital English letters plus a one-digit number), a positive number C (≤20) which is the number of courses that this student has registered, and then followed by C course numbers. For the sake of simplicity, the courses are numbered from 1 to K.

For each test case, print the student name lists of all the courses in increasing order of the course numbers. For each course, first print in one line the course number and the number of registered students, separated by a space. Then output the students’ names in alphabetical order. Each name occupies a line.

10 5 
ZOE1 2 4 5 
ANN0 3 5 2 1 
BOB5 5 3 4 2 1 5 
JOE4 1 2 
JAY9 4 1 2 5 4 
FRA8 3 4 2 5 
DON2 2 4 5 
AMY7 1 5 
KAT3 3 5 4 2 
LOR6 4 2 4 1 5 

1 4 
ANN0 
BOB5 
JAY9 
LOR6 
2 7 
ANN0 
BOB5 
FRA8 
JAY9 
JOE4 
KAT3 
LOR6 
3 1 
BOB5 
4 7 
BOB5 
DON2 
FRA8 
JAY9 
KAT3 
LOR6 
ZOE1 
5 9 
AMY7 
ANN0 
BOB5 
DON2 
FRA8 
JAY9 
KAT3 
LOR6 
ZOE1

#include <bits/stdc++.h>
using namespace std;
const int max_stu = 40001;   
const int max_course = 2501; //最大的课程数

vector<int> course[max_course]; //course[i]为第i门课的学生编号
char name[max_stu][5];

bool cmp(int a, int b)
{
    return strcmp(name[a], name[b]) < 0;
}

int main()
{
    int N, K;
    scanf("%d%d", &N, &K);
    int num, course_id; //选课的人数,课号
    for (int i = 0; i < N; i++)
    {
        scanf("%s%d", name[i], &num);
        for (int j = 0; j < num; j++)
        {
            scanf("%d", &course_id);
            course[course_id].push_back(i); //学生i加入course_id这门课
        }
    }

    for (int i = 1; i <= K; i++)
    {
        printf("%d %dn", i, course[i].size()); //第i门课的学生数
        sort(course[i].begin(), course[i].end(), cmp);
        for (int j = 0; j < course[i].size(); j++)
            printf("%sn", name[course[i][j]]);
    }

    return 0;
}