731. My Calendar II

You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a triple booking.

A triple booking happens when three events have some non-empty intersection (i.e., some moment is common to all the three 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 MyCalendarTwo class:

• MyCalendarTwo() 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 triple booking. Otherwise, return false and do not add the event to the calendar.

class MyCalendarTwo {
    map<int, int> m;
    bool doFailure(int start, int end) {
        m[start]--;
        m[end]++;

        if(!m[end]) m.erase(end);
        if(!m[start]) m.erase(start);

        return false;
    }
public:
    MyCalendarTwo() {}

    bool book(int start, int end) {
        m[start]++;
        m[end]--;
        int cnt = 0;
        for(auto [k, v]: m) {
            cnt += v;
            if(cnt >= 3) {
                return doFailure(start, end);
            }
        }

        return true;
    }
};

/**
 * Your MyCalendarTwo object will be instantiated and called as such:
 * MyCalendarTwo* obj = new MyCalendarTwo();
 * bool param_1 = obj->book(start,end);
 */