题解 | 牛牛学数列6
牛牛学数列6
https://www.nowcoder.com/practice/b6321648517247b2ac2e2f80cbc63ae1
#include <iostream>
using namespace std;
int main() {
int n=0,a1=0,a2=1,a3=1,an=0;
cin>>n;
if(n==1){
cout<<a1<<endl;
}
else if(n==2||n==3){
cout<<a2<<endl;
}
else{
for(int i=4;i<=n;i++){
an=a1+2*a2+a3;
a1=a2;
a2=a3;
a3=an;}
cout<<an<<endl;
}
return 0;
}
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