# My Calendar II

Implement a`MyCalendarTwo`class to store your events. A new event can be added if adding the event will not cause a **triple** booking.

Your class will have one 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`.

Atriple bookinghappens when **three** events have some non-empty intersection (ie., there is some time that is common to all 3 events.)

For each call to the method`MyCalendar.book`, return`true`if the event can be added to the calendar successfully without causing a **triple** 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(50, 60); // returns true
MyCalendar.book(10, 40); // returns true
MyCalendar.book(5, 15); // returns false
MyCalendar.book(5, 10); // returns true
MyCalendar.book(25, 55); // returns true

Explanation:

The first two events can be booked.  The third event can be double booked.
The fourth event (5, 15) can't be booked, because it would result in a triple booking.
The fifth event (5, 10) can be booked, as it does not use time 10 which is already double booked.
The sixth event (25, 55) can be booked, as the time in [25, 40) will be double booked with the third event;
the time [40, 50) will be single booked, and the time [50, 55) will be double booked with the second event.
```

## Note

其实是扫描线做法，start记为1，end记为-1，在TreeMap保持有序的前提下，累加value（count），如果count的值在某一个时间点比2大了，就不满足要求，同时更新map的值（包括remove）

## Code

```java
class MyCalendarTwo {
    TreeMap<Integer, Integer> delta;

    public MyCalendarTwo() {
        delta = new TreeMap();
    }

    public boolean book(int start, int end) {
        delta.put(start, delta.getOrDefault(start, 0) + 1);
        delta.put(end, delta.getOrDefault(end, 0) - 1);

        int active = 0;
        for (int d: delta.values()) {
            active += d;
            if (active >= 3) {
                delta.put(start, delta.get(start) - 1);
                delta.put(end, delta.get(end) + 1);
                if (delta.get(start) == 0)
                    delta.remove(start);
                return false;
            }
        }
        return true;
    }
}
```


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