From 740b1366e60f0033424099069e35af356ea8c383 Mon Sep 17 00:00:00 2001
From: Kirito <1362050620@qq.com>
Date: Mon, 24 Oct 2016 16:48:52 +0800
Subject: [PATCH] Create 1865.cpp

---
 QUSTOJ/1865.cpp | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 QUSTOJ/1865.cpp

diff --git a/QUSTOJ/1865.cpp b/QUSTOJ/1865.cpp
new file mode 100644
index 0000000..c230cd9
--- /dev/null
+++ b/QUSTOJ/1865.cpp
@@ -0,0 +1,22 @@
+#include <iostream>
+using namespace std;
+
+double ans[50];
+int vis[50];
+
+double dfunc(int n,int x)
+{
+    if(n==0) return 1;
+    if(n==1) return x;
+    if(vis[n]) return ans[n];
+    vis[n]=1;
+    return ans[n]=double((2*n-1)*x*dfunc(n-1,x)-(n-1)*dfunc(n-2,x))/n;
+}
+
+int main()
+{
+    int a,b;
+    cin>>a>>b;
+    cout<<dfunc(a,b);
+    return 0;
+}