0729. My Calendar I

https://leetcode.com/problems/my-calendar-i

Description

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.

ac1: TreeMap

class MyCalendar {
    TreeMap<Integer, Integer> tmap;
    public MyCalendar() {
        tmap = new TreeMap<>();
    }
    
    public boolean book(int start, int end) {
        Integer f = tmap.floorKey(start);
        Integer c = tmap.ceilingKey(start);
        if (f != null && tmap.get(f) > start || c != null && end > c) {
            return false;
        }
        tmap.put(start, end);
        return true;
    }
}
// O(logN) query and insert

Can be more concise:

TreeMap<Integer, Integer> map;
public MyCalendar() {
    map = new TreeMap<>();
}

public boolean book(int start, int end) {
    Integer low = map.lowerKey(end);
    
    if(low == null || map.get(low) <= start) {
        map.put(start, end);
        return true;
    }
    return false;
}

ac2: Doublely LinkedList + Binary Search

• Use Doublely LinkedList to store intervals;

• Binary search find insertion index of start, check if it's valid. Just like above TreeMap approach. Benefit: O(logN) lookup, O(1) insert. The code is lengthy though.