leetcode 729. My Calendar I（日程1）

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.

每段[start, end)表示日程是从start~end（不包含end), 日程不能有重叠的部分，
如果能加入日程，返回true, 否则false.

主要是判断每一段是否与已有的日程有重叠，
新进来的日程可以跟已有的每一段比较，
两段日程(s1, e1), (s2, e2)有重叠表示要么s2在s1 ~ e1之间，要么e2在s1 ~ e1之间。
没有重叠的话把新的日程加进去，返回true。

class MyCalendar {
    List> calendar;
    public MyCalendar() {
        calendar = new ArrayList<>();
    }
    
    public boolean book(int start, int end) {
        for(Pair tmp : calendar) {
            if(end > tmp.getKey() && start < tmp.getValue()) {
                return false;
            }           
        }
        calendar.add(new Pair(start, end));
        return true;
    }
}

还有一种beat 99%的方法，
构造一个类似双向链表的数据结构，每个节点是一个日程(start, end)
当没有重叠时：即s1 >= e1 或者 e2 <= s1时
要插入新的节点，通过移动链表的指针进行插入操作。

如果有重叠，直接返回false。

class MyCalendar {
    private class CalendarNode{
        int start;
        int end;
        CalendarNode next;
        CalendarNode prev;
        
        public CalendarNode(int start, int end){
            this.start = start;
            this.end = end;
        }
    }
    
    CalendarNode calendar;
    public MyCalendar() {
        calendar = null;
    }
    
    public boolean book(int start, int end) {
        if (calendar == null) {
            calendar = new CalendarNode(start, end);
            return true;
        } else {
            return insertNewCalendarNode(start, end);
        }
    }
    
    private boolean insertNewCalendarNode(int start, int end){
        CalendarNode cn = calendar;
        
        //没有重叠的情况
        while (end <= cn.start || start >= cn.end) {
            if (cn.start >= end) {
                if (cn.prev != null) {
                    cn = cn.prev;
                } else {
                    cn.prev = new CalendarNode(start, end);
                    return true;
                }
            } else if (cn.end <= start) {
                if (cn.next != null) {
                    cn = cn.next;
                } else {
                    cn.next = new CalendarNode(start, end);
                    return true;
                }
            }
        }
        
        return false;
    }
}