My Calendar I (M)

題目

Implement a MyCalendar class to store your events. A new event can be added if adding the event will not cause a double booking.

Your class will have the method, book(int start, int end). Formally, this represents a booking on the half open interval [start, end), the range of real numbers x

A double booking happens when two events have some non-empty intersection (ie., there is some time that is common to both events.)

For each call to the method MyCalendar.book, return true if the event can be added to the calendar successfully without causing a double booking. Otherwise, return false

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(15, 25); // returns false
MyCalendar.book(20, 30); // returns true
Explanation: 
The first event can be booked.  The second can't because time 15 is already booked by another event.
The third event can be booked, as the first event takes every time less than 20, but not including 20.
 

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].

題意

給定若干個區間範圍，依次加到日程中，每個區間不能重疊，判斷每次加入是否成功。

思路

建一個類似BST的樹即可，結點的值為區間範圍。

程式碼實現

Java

class MyCalendar {
    private Node root;
    private int size;

    public MyCalendar() {
        root = null;
        size = 0;
    }

    public boolean book(int start, int end) {
        int old = size;
        root = insert(root, start, end);
        return size == old + 1;
    }

    private Node insert(Node root, int start, int end) {
        if (root == null) {
            size++;
            return new Node(start, end);
        }

        if (start >= root.end) {
            root.right = insert(root.right, start, end);
        } else if (end <= root.start) {
            root.left = insert(root.left, start, end);
        }

        return root;
    }

    class Node {
        int start, end;
        Node left, right;

        Node(int start, int end) {
            this.start = start;
            this.end = end;
        }
    }
}