PAT 甲级 1006. Sign In and Sign Out

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本文介绍了一个使用C++实现的签到系统案例，该系统能够记录人员的签到和签退时间，并通过算法确定每天第一个签到（解锁门）和最后一个签退（锁门）的人员。采用自定义比较函数配合标准库sort函数完成人员的排序。

原题传送门

< algorithm >中的sort()用法

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

struct info {
    string ID_number;
    string Sign_in_time;
    string Sign_out_time;

};

bool MyUnlock(info lhs, info rhs) {   // 升序
    return lhs.Sign_in_time < rhs.Sign_in_time;
}

bool MyLock(info lhs, info rhs) { // 降序
    return lhs.Sign_out_time > rhs.Sign_out_time;
}

int main(int argc, const char * argv[]) {
    info I;
    string ID_number, Sign_in_time, Sign_out_time;
    vector<info> vec;
    int M;
    cin >> M;
    for(int i = 0; i < M; ++i) {
        cin >> ID_number >> Sign_in_time >> Sign_out_time;
        I.ID_number = ID_number;
        I.Sign_in_time = Sign_in_time;
        I.Sign_out_time = Sign_out_time;
        vec.push_back(I);
    }

    string unlock_ID, lock_ID;
    std::sort(vec.begin(), vec.end(), MyUnlock);
    unlock_ID = (*vec.begin()).ID_number;
    std::sort(vec.begin(), vec.end(), MyLock);
    lock_ID = (*vec.begin()).ID_number;
    cout << unlock_ID << " " << lock_ID;
    cout << endl;

    return 0;
}

附原题：

At the beginning of every day, the first person who signs in the computer room will unlock the door, and the last one who signs out will lock the door. Given the records of signing in’s and out’s, you are supposed to find the ones who have unlocked and locked the door on that day.

Input Specification:

Each input file contains one test case. Each case contains the records for one day. The case starts with a positive integer M, which is the total number of records, followed by M lines, each in the format:

ID_number Sign_in_time Sign_out_time
where times are given in the format HH:MM:SS, and ID number is a string with no more than 15 characters.

Output Specification:

For each test case, output in one line the ID numbers of the persons who have unlocked and locked the door on that day. The two ID numbers must be separated by one space.

Note: It is guaranteed that the records are consistent. That is, the sign in time must be earlier than the sign out time for each person, and there are no two persons sign in or out at the same moment.

Sample Input:
3
CS301111 15:30:28 17:00:10
SC3021234 08:00:00 11:25:25
CS301133 21:45:00 21:58:40
Sample Output:
SC3021234 CS301133