LeetCode-in-Java

729. My Calendar I

Medium

You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking.

A double booking happens when two events have some non-empty intersection (i.e., some moment is common to both events.).

The event can be represented as a pair of integers start and end that represents a booking on the half-open interval [start, end), the range of real numbers x such that start <= x < end.

Implement the MyCalendar class:

• MyCalendar() Initializes the calendar object.
• boolean book(int start, int end) Returns true if the event can be added to the calendar successfully without causing a double booking. Otherwise, return false and do not add the event to the calendar.

Example 1:

Input

[“MyCalendar”, “book”, “book”, “book”]

[[], [10, 20], [15, 25], [20, 30]]

Output: [null, true, false, true]

Explanation:

MyCalendar myCalendar = new MyCalendar(); 
myCalendar.book(10, 20); // return True 
myCalendar.book(15, 25); // return False, It can not be booked because time 15 is already booked by another event. 
myCalendar.book(20, 30); // return True, The event can be booked, as the first event takes every time less than 20, but not including 20.

Constraints:

• 0 <= start < end <= 109
• At most 1000 calls will be made to book.

Solution

import java.util.TreeSet;

@SuppressWarnings("java:S1210")
public class MyCalendar {
    static class Meeting implements Comparable<Meeting> {
        public final int start;
        public final int end;

        public Meeting(int start, int end) {
            this.start = start;
            this.end = end;
        }

        @Override
        public int compareTo(Meeting anotherMeeting) {
            return this.start - anotherMeeting.start;
        }
    }

    private final TreeSet<Meeting> meetings;

    public MyCalendar() {
        meetings = new TreeSet<>();
    }

    public boolean book(int start, int end) {
        Meeting meetingToBook = new Meeting(start, end);
        Meeting prevMeeting = meetings.floor(meetingToBook);
        Meeting nextMeeting = meetings.ceiling(meetingToBook);
        if ((prevMeeting == null || prevMeeting.end <= meetingToBook.start)
                && (nextMeeting == null || meetingToBook.end <= nextMeeting.start)) {

            meetings.add(meetingToBook);
            return true;
        }
        return false;
    }
}

/*
 * Your MyCalendar object will be instantiated and called as such:
 * MyCalendar obj = new MyCalendar();
 * boolean param_1 = obj.book(start,end);
 */

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