PAT 解题报告 1047. Student List for Course (25)

1047. Student List for Course (25)

Zhejiang University has 40000 students and provides 2500 courses. Now given the registered course list of each student, you are supposed to output the student name lists of all the courses.

Input Specification:

Each input file contains one test case. For each case, the first line contains 2 numbers: N (<=40000), the total number of students, and K (<=2500), 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.

Output Specification:

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.

Sample Input:

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

Sample Output:

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

题意

根据每名学生填报的课程，按顺序输出每门课程的学生名单。其中学生总量为 N(<=40000)，课程总量为 K(<=2500)。学生姓名为 3 个大写英文字符加一个数字。

分析

倒排索引的模拟。可以针对学生姓名做 hash 方式的优化。

容易超时，vector<string>能飘过。

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;

vector<string> vs[2501];

int main()
{
    int N,M;
    scanf("%d%d", &N, &M);
    for (int i=0; i<N; i++) {
        char cs[6];
        int c;
        scanf("%s%d", cs, &c);
        string name = cs;
        for (int j=0; j<c ;j++){
            int id;
            scanf("%d", &id);
            vs[id].push_back(name);
        }
    }

    for (int i=1; i<=M; i++) {
        vector<string> & v = vs[i];
        printf("%d %d
", i, v.size());
        sort(v.begin(), v.end());
        for (int j=0; j<v.size(); j++) {
            printf("%s
", v[j].c_str());
        }
    }

    return 0;
}