My Calendar I

Implement a MyCalendar class to store your events. A new event can be added if adding the event will not cause a double booking.

Your class will have the method, book(int start, int end). Formally, this represents a booking on the half open interval [start, end), the range of real numbers x such that start <= x < end. A double booking happens when two events have some non-empty intersection (ie., there is some time that is common to both events.)

For each call to the method, return 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.Your class will be called like this: MyCalendar cal = new MyCalendar();, end)

Example 1:

MyCalendar();, 20); // returns true, 25); // returns false, 30); // returns true
The first event can be booked.  The second can't because time 15 is already booked by another event.
The third event can be booked, as the first event takes every time less than 20, but not including 20.​

You can book an appointment only if the start of the current appointment is greater or equal to the end of the last appointment and the end of the current appointment is less than or equal to the next appointment. We need a data structure that keeps elements sorted and supports fast insertion. In Java, a TreeMap is the perfect candidate. We will have a TreeMap where the keys are the start of each interval, and the values are the ends of those intervals. We have used the floorKey() and ceilingKey() method of TreeMap to implement the algorithm.

import java.util.TreeMap;
 class MyCalendar {
   TreeMap<Integer,Integer> calender;
   public MyCalendar() {
     calender = new TreeMap<>();
   public boolean book(int start, int end) {
     Integer lastKey = calender.floorKey(start);
     Integer nextKey = calender.ceilingKey(start);
      * You can book an appointment only if the start of
      * current appointment is greater or equal to the end
      * of last appointment and the end of current appointment
      * is less than or equal to the next appointment.
     if ((lastKey == null || calender.get(lastKey) <= start) &&
       (nextKey == null || nextKey >= end)) {
       calender.put(start, end);
       return true;
     return false;
 public class MyCalendar_1 {
   public static void main(String[] args) {
     MyCalendar myCalendar = new MyCalendar();
     System.out.println("Book the slot :" +, 20));
     System.out.println("Book the slot :" +, 25));
     System.out.println("Book the slot :" +, 30));

Complexity Analysis

  • Time Complexity: O(NlogN), where N is the number of events booked. For each new event, we search that the event is in O(logN) time, then insert it in O(1) time.
  • Space Complexity: O(N), the size of the TreeMap.

Categories: Map

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