# 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.

&#x20;

**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.
```

&#x20;

**Constraints:**

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

```python
class Node:
    def __init__(self, start, end):
        self.start = start
        self.end = end
        self.left = None
        self.right = None
        
class MyCalendar:

    def __init__(self):
        self.root = None
    
    def helper(self, start, end, node):
        if start >= node.end:
            if node.right:
                return self.helper(start, end, node.right)
            else:
                node.right = Node(start, end)
                return True
        elif end <= node.start:
            if node.left:
                return self.helper(start, end, node.left)
            else:
                node.left = Node(start, end)
                return True
        return False
        

    def book(self, start: int, end: int) -> bool:
        if not self.root:
            self.root = Node(start,end)
            return True
        return self.helper(start, end, self.root)
```