LeetCode #731 - My Calendar II

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本文介绍了一个名为MyCalendarTwo的类的实现，该类用于存储事件，并确保在添加新事件时不会导致三次预订冲突。文章详细解释了如何通过使用两个集合s1和s2来跟踪所有事件和重叠事件，从而避免三次预订。通过示例展示了类的使用方法。

题目描述：

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].

class MyCalendarTwo {
public:
    MyCalendarTwo() {}
    // 在本题中不能用二分法查找区间判断是否有交集，因为我们并没有对交叉的区间合并，而是把他们全部加入s1/s2中
    // 所以只查找lower_bound两边的集合是不够的，因此只能遍历集合中全部区间
    bool book(int start, int end) {
        pair<int,int> p={start,end};
        // 判断新区间是否和s2不交叉，如果交叉返回false
        for(auto x : s2)
            if (isIntersect(x,p)) return false;
        // 发现新区间和s2不交叉，再判断是否和s1交叉，将交集加入s2中，整个区间加入s1中
        for(auto x : s1)
        {
            if(isIntersect(x,p)) 
                s2.insert({max(start,x.first), min(end,x.second)});
        }
        s1.insert(p);
        return true;
    }
    
    bool isIntersect(pair<int,int> a, pair<int,int> b)
    {
        if(a.second<=b.first||b.second<=a.first) return false;
        else return true;
    }
    
private:
    set<pair<int,int>> s1; // 全部区间
    set<pair<int,int>> s2; // 交叉区间的交集，这一范围内的所有数字都已经出现两次
};
/**
 * Your MyCalendarTwo object will be instantiated and called as such:
 * MyCalendarTwo obj = new MyCalendarTwo();
 * bool param_1 = obj.book(start,end);
 */