# 731. My Calendar II

[ **731. My Calendar II**](https://leetcode.com/problems/my-calendar-ii/description/)

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`.

A triple booking happens 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:**

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]`.

***My Solutions:***

和上题729方法1思路类似，但是因为可以重叠一次，所以需要用两个list来储存。一个储存已经overlap过的区域，这个区域不能再重叠。另一个储存所有输入的合法区域

old.start < end && start < old.end 表示两个区域重叠

```java
public class MyCalendar {
    List<int[]> calendar;
    List<int[]> overlaps;

    MyCalendar() {
        overlaps = new ArrayList();
        calendar = new ArrayList();
    }

    public boolean book(int start, int end) {
        for (int[] interval: overlaps) {
            if (interval[0] < end && start < interval[1]) return false;
        }
        for (int[] interval: calendar) {
            if (interval[0] < end && start < interval[1]) {
                overlaps.add(new int[]{Math.max(start, interval[0]), Math.min(end, interval[1])});
            }
        }
        calendar.add(new int[]{start, end});
        return true;
    }
}
```
