Formatted question description: https://leetcode.ca/all/729.html

Level

Medium

Description

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 MyCalendar.book, 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(); MyCalendar.book(start, end)

Example 1:

MyCalendar();
MyCalendar.book(10, 20); // returns true
MyCalendar.book(15, 25); // returns false
MyCalendar.book(20, 30); // returns true
Explanation: 
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.

Note:

  • The number of calls to MyCalendar.book per test case will be at most 1000.
  • In calls to MyCalendar.book(start, end), start and end are integers in the range [0, 10^9].

Solution

Use a list to store the intervals of booking, which contains all intervals in sorted order. Each time book(int start, int end) is called, loop over the list of intervals to see whether the new interval [start, end) can be added.

If the new interval can be added at the start or at the end without causing a double booking, add the new interval at the start or at the end and return true.

If the new interval can be added between two intervals without causing a double booking, add the new interval between the two intervals and return true.

If the new interval has intersection with any interval in the list, then adding the interval will cause double booking, so return false.

Java

import java.util.TreeMap;

public class My_Calendar_I {

    public static void main (String[] args) {
        My_Calendar_I out = new My_Calendar_I();
        MyCalendar c = out.new MyCalendar();

//        System.out.println(c.book(20,29));
//        System.out.println(c.book(13,22));
//        System.out.println(c.book(44,50));
//        System.out.println(c.book(1,7));
//        System.out.println(c.book(2,10));
//        System.out.println(c.book(14,20));
//        System.out.println(c.book(19,25));
//        System.out.println(c.book(36,42));
//        System.out.println(c.book(45,50));


        System.out.println(c.book(0,6));
        System.out.println(c.book(0,7));

        // test on TreeMap
        TreeMap<Integer, Integer> tm = new TreeMap<>();
        tm.put(3, 10);
        tm.put(5, 110);
        tm.put(7, 150);
        System.out.println(tm.ceilingKey(4)); // output: 5
        System.out.println(tm.floorKey(4)); // output: 3
        System.out.println(tm.floorKey(1)); // output: null
        // @memorize: cannot use `int`, should use `Integer`
        int floor = tm.floorKey(1);
        System.out.println(floor); // output: java.lang.NullPointerException
    }


    // ref: https://leetcode.com/problems/my-calendar-i/solution/
    //      https://leetcode.com/articles/my-calendar-i/
    class MyCalendar {

        // each element is start->end pair
        TreeMap<Integer, Integer> startEndMap;

        public MyCalendar() {
            startEndMap = new TreeMap<>();
        }

        public boolean book(int start, int end) {

            // Returns the greatest key less than or equal to the given key, or null
            Integer prevStart = startEndMap.floorKey(start); // @note: Integer, not int, for later null check

            // Returns the least key greater than or equal to the given key, or null
            Integer nextStart = startEndMap.ceilingKey(start);

            if (
                    (prevStart == null || startEndMap.get(prevStart) <= start) // get will return end date
                    && (nextStart == null || end <= nextStart)
               ) {
                startEndMap.put(start, end);
                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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