cs: add «729. My Calendar I»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/my-calendar-i.cs

@@ -0,0 +1,41 @@
+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;
+    }
+}