From abb3305568e8bda7a7661bbae5281a0596c84d8b Mon Sep 17 00:00:00 2001
From: Lam Haoyin <root@eatswap.org>
Date: Sun, 6 Mar 2022 10:19:51 +0800
Subject: [PATCH] add: 220306 [cpp]

---
 cpp/2203/220306.cpp     | 25 +++++++++++++++++++++++++
 cpp/2203/CMakeLists.txt |  2 +-
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 cpp/2203/220306.cpp

diff --git a/cpp/2203/220306.cpp b/cpp/2203/220306.cpp
new file mode 100644
index 0000000..670dff7
--- /dev/null
+++ b/cpp/2203/220306.cpp
@@ -0,0 +1,25 @@
+#include <iostream>
+
+class Solution {
+private:
+	inline static const int MOD = 1000000007;
+public:
+	// OEIS A000680		a(n) = (2n)!/2^n.
+	static constexpr int countOrders(int n) {
+		if (n == 1)
+			return 1;
+		if (n == 2)
+			return 6;
+		unsigned long long ret = 6;
+		for (int i = 3; i <= n; ++i) {
+			ret = (ret * i) % MOD;
+			ret = (ret * ((i << 1) - 1)) % MOD;
+		}
+		return ret % MOD;
+	}
+};
+
+int main() {
+	std::cout << Solution::countOrders(5);
+	return 0;
+}
diff --git a/cpp/2203/CMakeLists.txt b/cpp/2203/CMakeLists.txt
index 118e96b..3b7275a 100644
--- a/cpp/2203/CMakeLists.txt
+++ b/cpp/2203/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2203)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2203 220306-CN.cpp)
+ADD_EXECUTABLE(2203 220306.cpp)