CSES 2. Movie Festival II (1632)

출처: https://cses.fi/problemset/task/1632

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문제 설명

In a movie festival, n movies will be shown.  movie club consists of k members, who will be all attending the festival.

You know the starting and ending time of each movie. What is the maximum total number of movies the club members can watch entirely if they act optimally?

입력 

The first input line has two integers n and k: the number of movies and club members.

After this, there are n lines that describe the movies. Each line has two integers aa and bb: the starting and ending time of a movie.

출력

Print one integer: the maximum total number of movies.

입력 예

5 2
1 5
8 10
3 6
2 5
6 9

출력 예

4

제약조건

• 1 <= k <= n <= 2x10^5
• 1 <= a <= b <= 10^9

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문제 풀이 내용

입력받은 영화 시작시간과 끝나는 시간을 이용해서, (영화시간, 시작/끝, 영화순서) 를 영화시간을 기준으로 정렬한다. 영화시작시간이면 클럽 맴버를 보내고, 끝나는 시간이면 본 영화수를 증가시키고, 영화 보고 있는 클럽 맴버수를 감소 시킨다.  

프로그램 내용

...
    vector <tuple<int, int>> m_time;

    for(int idx=0; idx < n_movie; ++idx)
        cin >> start_time >> end_time ;
        m_time.push_back({end_time, start_time});

    sort(m_time.begin(), m_time.end(), greater<tuple<int, int>>());

    vector<tuple<int, bool, int>> m_schedule(2*n_movie);

    for (int idx = 0; idx < n_movie; ++idx)
        tie(end_time, start_time) = m_time[idx];
        m_schedule[2*idx] = {start_time, 0, idx};
        m_schedule[2*idx + 1] = {end_time, 1, idx};

    sort(m_schedule.begin(), m_schedule.end());

    set <int> c_movie;
    int ct_member=0;
    int ct_movie=0;

    for (int idx=0; idx < 2*n_movie; ++idx)
        int m_time, m_idx;
        bool flag;
        tie(m_time,flag,m_idx) = m_schedule[idx];

        if(!flag) /// flag == 0, movie start time -> club member see
            c_movie.insert(m_idx);
            ct_member++;
        else if( c_movie.count(m_idx)) /// movie end,
            c_movie.erase(m_idx);
            ct_member--;
            ct_movie++;

        if ( idx < 2*n_movie -1 && get<0>(m_schedule[idx+1]) == m_time)
            continue;

        if (ct_member > n_member) /// can not exceed max member
            c_movie.erase(c_movie.begin());
            ct_member--;
...

 

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