731

731. My Calendar II (Medium)

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.

 

Example 1:

Input
["MyCalendarTwo", "book", "book", "book", "book", "book", "book"]
[[], [10, 20], [50, 60], [10, 40], [5, 15], [5, 10], [25, 55]]
Output
[null, true, true, true, false, true, true]

Explanation
MyCalendarTwo myCalendarTwo = new MyCalendarTwo();
myCalendarTwo.book(10, 20); // return True, The event can be booked. 
myCalendarTwo.book(50, 60); // return True, The event can be booked. 
myCalendarTwo.book(10, 40); // return True, The event can be double booked. 
myCalendarTwo.book(5, 15);  // return False, The event ca not be booked, because it would result in a triple booking.
myCalendarTwo.book(5, 10); // return True, The event can be booked, as it does not use time 10 which is already double booked.
myCalendarTwo.book(25, 55); // return True, The event 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.

 

Constraints:

• 0 <= start < end <= 109
• At most 1000 calls will be made to book.

Companies:
Google, Microsoft, Amazon

Related Topics:
Design, Segment Tree, Ordered Set

Similar Questions:

• My Calendar I (Medium)
• My Calendar III (Hard)

Solution 1. Difference Array

// OJ: https://leetcode.com/problems/my-calendar-ii/
// Author: github.com/lzl124631x
// Time:
//      MyCalendarTwo: O(1)
//      book: O(N)
// Space: O(N)
class MyCalendarTwo {
    map<int, int> m; // number -> diff
public:
    MyCalendarTwo() {}
    bool book(int start, int end) {
        m[start]++;
        m[end]--;
        int sum = 0;
        for (auto &[n, d] : m) {
            sum += d;
            if (sum > 2) {
                if (--m[start] == 0) m.erase(start);
                if (++m[end] == 0) m.erase(end);
                return false;
            }
        }
        return true;
    }
};