题目描述：

LeetCode 729. My Calendar I

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].

题目大意：

实现MyCalendar类，存储一组互不冲突的活动。

函数book(start, end)输入一个活动的起止时间，若该活动不与现有活动冲突，添加并返回true。否则返回false。

解题思路：

TreeMap（红黑树）

判断拟增加活动的起始时间是否与其相邻活动的时间冲突

Java代码：

class MyCalendar {

    private TreeMap<Integer, Integer> startMap;
    public MyCalendar() {
        startMap = new TreeMap<>();
    }
    
    public boolean book(int start, int end) {
        Integer nextStart = startMap.ceilingKey(start);
        if (nextStart != null && nextStart < end) {
            return false;
        }
        Integer prevStart = startMap.lowerKey(start);
        if(prevStart != null && startMap.get(prevStart) > start) {
            return false;
        }
        startMap.put(start, end);
        return true;
    }

}

/**
 * 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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