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2402. Meeting Rooms III 👍

  • Time: $O(\texttt{sort}(\texttt{meetings}))$
  • Space: $O(n)$
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struct T {
  long endTime;
  int roomId;
};

class Solution {
 public:
  int mostBooked(int n, vector<vector<int>>& meetings) {
    vector<int> count(n);

    ranges::sort(meetings);

    auto compare = [](const T& a, const T& b) {
      return a.endTime == b.endTime ? a.roomId > b.roomId
                                    : a.endTime > b.endTime;
    };
    priority_queue<T, vector<T>, decltype(compare)> occupied(compare);
    priority_queue<int, vector<int>, greater<>> availableRoomIds;

    for (int i = 0; i < n; ++i)
      availableRoomIds.push(i);

    for (const vector<int>& meeting : meetings) {
      const int start = meeting[0];
      const int end = meeting[1];
      // Push meetings ending before this `meeting` in occupied to the
      // `availableRoomsIds`.
      while (!occupied.empty() && occupied.top().endTime <= start)
        availableRoomIds.push(occupied.top().roomId), occupied.pop();
      if (availableRoomIds.empty()) {
        const auto [newStart, roomId] = occupied.top();
        occupied.pop();
        ++count[roomId];
        occupied.push({newStart + (end - start), roomId});
      } else {
        const int roomId = availableRoomIds.top();
        availableRoomIds.pop();
        ++count[roomId];
        occupied.push({end, roomId});
      }
    }

    return ranges::max_element(count) - count.begin();
  }
};

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class T {
  public long endTime;
  public int roomId;
  public T(long endTime, int roomId) {
    this.endTime = endTime;
    this.roomId = roomId;
  }
}

class Solution {
  public int mostBooked(int n, int[][] meetings) {
    int[] count = new int[n];

    Arrays.sort(meetings, (a, b) -> Integer.compare(a[0], b[0]));

    Queue<T> occupied =
        new PriorityQueue<>((a, b)
                                -> a.endTime == b.endTime ? Integer.compare(a.roomId, b.roomId)
                                                          : Long.compare(a.endTime, b.endTime));
    Queue<Integer> availableRoomIds = new PriorityQueue<>();

    for (int i = 0; i < n; ++i)
      availableRoomIds.offer(i);

    for (int[] meeting : meetings) {
      final int start = meeting[0];
      final int end = meeting[1];
      // Push meetings ending before this `meeting` in occupied to the
      // `availableRoomsIds`.
      while (!occupied.isEmpty() && occupied.peek().endTime <= start)
        availableRoomIds.offer(occupied.poll().roomId);
      if (availableRoomIds.isEmpty()) {
        T t = occupied.poll();
        ++count[t.roomId];
        occupied.offer(new T(t.endTime + (end - start), t.roomId));
      } else {
        final int roomId = availableRoomIds.poll();
        ++count[roomId];
        occupied.offer(new T(end, roomId));
      }
    }

    int maxIndex = 0;
    for (int i = 0; i < n; ++i)
      if (count[i] > count[maxIndex])
        maxIndex = i;
    return maxIndex;
  }
}

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class Solution:
  def mostBooked(self, n: int, meetings: list[list[int]]) -> int:
    count = [0] * n

    meetings.sort()

    occupied = []  # (endTime, roomId)
    availableRoomIds = [i for i in range(n)]
    heapq.heapify(availableRoomIds)

    for start, end in meetings:
      # Push meetings ending before this `meeting` in occupied to the
      # `availableRoomsIds`.
      while occupied and occupied[0][0] <= start:
        heapq.heappush(availableRoomIds, heapq.heappop(occupied)[1])
      if availableRoomIds:
        roomId = heapq.heappop(availableRoomIds)
        count[roomId] += 1
        heapq.heappush(occupied, (end, roomId))
      else:
        newStart, roomId = heapq.heappop(occupied)
        count[roomId] += 1
        heapq.heappush(occupied, (newStart + (end - start), roomId))

    return count.index(max(count))