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history_source/ccf 基础篇/U1/1.6.3.cpp

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+#include<iostream>
+using namespace std;
+long double f_j(int sr)
+{
+    if(sr<0) return 0;
+    if(sr==0) return 1;
+    return sr*f_j(sr-1);
+}
+long double C(int x,int y)
+{
+    return f_j(x)/f_j(x-y)/f_j(y);
+}
+long double big_(long double a,long double b)
+{
+return (a>b)?a:b;
+}
+long double small_(long double a,long double b)
+{
+return (a<b)?a:b;
+}
+int main()
+{
+	int n,add;
+	while(true)
+	{
+		cin>>n;
+		add=0;
+		for(int one=0;one<=n;one++)
+		{
+			for(int two=0;two<=n/2;two++)
+			{
+				if(one+two*2==n)
+				{
+					add+=C(big_(one,two)+small_(one,two),small_(one,two));
+				}
+			}
+		}
+		cout<<add<<endl;
+	}
+}