LeetCode/cs/my-calendar-i.cs

public class MyCalendar {
    private record Meeting(int Start, int End) {
        public bool Has(int x) => x > Start && x < End;

        public static bool operator <(Meeting a, Meeting b) => a.Start < b.Start;
        public static bool operator >(Meeting a, Meeting b) => a.Start > b.Start;
    }

    private static bool Overlaps(Meeting a, Meeting b)
        => a == b || a.Has(b.Start) || a.Has(b.End) || b.Has(a.Start) || b.Has(a.End);

    private List<Meeting> meetings = [];

    public MyCalendar() { }

    public bool Book(int start, int end) {
        meetings.Add(new Meeting(start, end));

        var it = meetings.Count - 1;

        for (
            int i = meetings.Count - 1;
            i > 0 && meetings[i - 1] > meetings[i];
            --i, --it
        ) {
            if (Overlaps(meetings[i], meetings[i - 1])) {
                meetings.RemoveAt(it);
                return false;
            }

            (meetings[i], meetings[i - 1]) = (meetings[i - 1], meetings[i]);
        }

        if (it > 0 && Overlaps(meetings[it], meetings[it - 1])) {
            meetings.RemoveAt(it);
            return false;
        }

        return true;
    }
}