feat: add cs solution to lc problem: No.1845

solution/1800-1899/1845.Seat Reservation Manager/README.md

@@ -197,6 +197,38 @@ func (h *hp) Pop() interface{} {
  */
 ```
 
+### **C#**
+
+```cs
+public class SeatManager {
+    private SortedSet<int> availableSeats;
+
+    public SeatManager(int n) {
+        availableSeats = new SortedSet<int>();
+        for (int i = 1; i <= n; i++) {
+            availableSeats.Add(i);
+        }
+    }
+
+    public int Reserve() {
+        int reservedSeat = availableSeats.Min;
+        availableSeats.Remove(reservedSeat);
+        return reservedSeat;
+    }
+
+    public void Unreserve(int seatNumber) {
+        availableSeats.Add(seatNumber);
+    }
+}
+
+/**
+ * Your SeatManager object will be instantiated and called as such:
+ * SeatManager obj = new SeatManager(n);
+ * int param_1 = obj.Reserve();
+ * obj.Unreserve(seatNumber);
+ */
+```
+
 ### **...**
 
 ```

solution/1800-1899/1845.Seat Reservation Manager/README_EN.md

@@ -176,6 +176,38 @@ func (h *hp) Pop() interface{} {
  */
 ```
 
+### **C#**
+
+```cs
+public class SeatManager {
+    private SortedSet<int> availableSeats;
+
+    public SeatManager(int n) {
+        availableSeats = new SortedSet<int>();
+        for (int i = 1; i <= n; i++) {
+            availableSeats.Add(i);
+        }
+    }
+
+    public int Reserve() {
+        int reservedSeat = availableSeats.Min;
+        availableSeats.Remove(reservedSeat);
+        return reservedSeat;
+    }
+
+    public void Unreserve(int seatNumber) {
+        availableSeats.Add(seatNumber);
+    }
+}
+
+/**
+ * Your SeatManager object will be instantiated and called as such:
+ * SeatManager obj = new SeatManager(n);
+ * int param_1 = obj.Reserve();
+ * obj.Unreserve(seatNumber);
+ */
+```
+
 ### **...**
 
 ```

solution/1800-1899/1845.Seat Reservation Manager/Solution.cs

@@ -0,0 +1,27 @@
+public class SeatManager {
+    private SortedSet<int> availableSeats;
+
+    public SeatManager(int n) {
+        availableSeats = new SortedSet<int>();
+        for (int i = 1; i <= n; i++) {
+            availableSeats.Add(i);
+        }
+    }
+
+    public int Reserve() {
+        int reservedSeat = availableSeats.Min;
+        availableSeats.Remove(reservedSeat);
+        return reservedSeat;
+    }
+
+    public void Unreserve(int seatNumber) {
+        availableSeats.Add(seatNumber);
+    }
+}
+
+/**
+ * Your SeatManager object will be instantiated and called as such:
+ * SeatManager obj = new SeatManager(n);
+ * int param_1 = obj.Reserve();
+ * obj.Unreserve(seatNumber);
+ */