My-Calendar-III

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题目地址

LeetCode#732 My Calendar III

题目描述

  Implement a MyCalendarThree class to store your events. A new event can always be added.

  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 K-booking happens when K events have some non-empty intersection (ie., there is some time that is common to all K events.)

  For each call to the method MyCalendar.book, return an integer K representing the largest integer such that there exists a K-booking in the calendar.

Your class will be called like this: 

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MyCalendarThree cal = new MyCalendarThree();
MyCalendarThree.book(start, end)

Example 1:

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MyCalendarThree();
MyCalendarThree.book(10, 20); // returns 1
MyCalendarThree.book(50, 60); // returns 1
MyCalendarThree.book(10, 40); // returns 2
MyCalendarThree.book(5, 15); // returns 3
MyCalendarThree.book(5, 10); // returns 3
MyCalendarThree.book(25, 55); // returns 3
Explanation: 
The first two events can be booked and are disjoint, so the maximum K-booking is a 1-booking.
The third event [10, 40) intersects the first event, and the maximum K-booking is a 2-booking.
The remaining events cause the maximum K-booking to be only a 3-booking.
Note that the last event locally causes a 2-booking, but the answer is still 3 because
eg. [10, 20), [10, 40), and [5, 15) are still triple booked.

Note:

  The number of calls to MyCalendarThree.book per test case will be at most 400.

  In calls to MyCalendarThree.book(start, end), start and end are integers in the range [0, 10^9].

解题思路

  题目要求实现一个类，类的book方法每次传入一个事件的起始时间和结束时间，然后返回当前所存在的所有事件的最多相交次数，即i时间点上有N个事件发生，求max(N0,N1,N2….Ni)。

  这个精妙的思路是参考网上的，我们构建一个map用来存储时间点和时间点对应的事件个数，每当遇到起始时间，则给起始时间的事件个数加1，给结束时间的事件个数减一，最终求和。

解题代码【.CPP】

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class MyCalendarThree {
private:
    map<int, int> freq;
public:
    MyCalendarThree() {}

    int book(int start, int end) {
        ++freq[start];
        --freq[end];
        int cnt = 0, mx = 0;
        for (auto f : freq) {
            cnt += f.second;
            mx = max(mx, cnt);
        }
        return mx;
    }
};

/**
 * Your MyCalendarThree object will be instantiated and called as such:
 * MyCalendarThree obj = new MyCalendarThree();
 * int param_1 = obj.book(start,end);
 */
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