PAT 1039 Course List for Student (25分)（哈希）-CFANZ编程社区

1039 Course List for Student (25分)

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

Input Specification:

Each input file contains one test case. For each case, the first line contains 2 positive integers: N (≤40,000), the number of students who look for their course lists, and K (≤2,500), the total number of courses. Then the student name lists are given for the courses (numbered from 1 to K) in the following format: for each course i, first the course index i and the number of registered students Ni (≤200) are given in a line. Then in the next line, Ni student names are given. A student name consists of 3 capital English letters plus a one-digit number. Finally the last line contains the N names of students who come for a query. All the names and numbers in a line are separated by a space.

Output Specification:

For each test case, print your results in N lines. Each line corresponds to one student, in the following format: first print the student's name, then the total number of registered courses of that student, and finally the indices of the courses in increasing order. The query results must be printed in the same order as input. All the data in a line must be separated by a space, with no extra space at the end of the line.

Sample Input:

11 5
4 7
BOB5 DON2 FRA8 JAY9 KAT3 LOR6 ZOE1
1 4
ANN0 BOB5 JAY9 LOR6
2 7
ANN0 BOB5 FRA8 JAY9 JOE4 KAT3 LOR6
3 1
BOB5
5 9
AMY7 ANN0 BOB5 DON2 FRA8 JAY9 KAT3 LOR6 ZOE1
ZOE1 ANN0 BOB5 JOE4 JAY9 FRA8 DON2 AMY7 KAT3 LOR6 NON9

Sample Output:

ZOE1 2 4 5
ANN0 3 1 2 5
BOB5 5 1 2 3 4 5
JOE4 1 2
JAY9 4 1 2 4 5
FRA8 3 2 4 5
DON2 2 4 5
AMY7 1 5
KAT3 3 2 4 5
LOR6 4 1 2 4 5
NON9 0

题意很容易理解，就是统计学生的课程列表

很容易的能够想出用 map，map<string, set<int>> mapp;

但是最后一个测试点就是超时过不去，

最后参考柳神的讲解，string比较卡时间

所以采用哈希，为什么采用哈希呢？因为每个人的名字都有固定的格式，而且不会存在同名现象，所以我们就可以指定一个哈希规则，求出每个名字的哈希值，所以 map 最后变成了 map<int, set<int> > mapp;

代码：

#include <bits/stdc++.h>
using namespace std;
int n, k;
//A student name consists of 3 capital English letters plus a one-digit number.
int hashId(string name){
  int id = 0;
  for(int i = 0; i < 3; i++){
    id = 26 * id + (name[i] - 'A');
  }
  id += id * 10 + (name[3] - '0');
  return id;
}
int main(){
  ios::sync_with_stdio(false);
  int Ki, Ni;
  string name;
  map<int, set<int> > mapp;
  set<int>::iterator sit;
  cin >> n >> k;
  for(int i = 0; i < k; i++){
    cin >> Ki >> Ni;
    for(int j = 0; j < Ni; j++){
      cin >> name;
      mapp[hashId(name)].insert(Ki); 
    }
  }
  int hashCode;
  for(int i = 0; i < n; i++){
    cin >> name; hashCode = hashId(name);
    cout << name << " " << mapp[hashCode].size();
  
    for(sit = mapp[hashCode].begin(); sit != mapp[hashCode].end(); sit++){
      cout << " " << (*sit);
    }
    cout << endl;
  }
  return 0;
}