hdu---2802---F(N)
题目链接: http://acm.split.hdu.edu.cn/showproblem.php?pid=2802
Problem Description
![](http://acm.split.hdu.edu.cn/data/images/C177-1003-1.gif)
Input
Each test case contains a single integer N(1<=N<=10^9). The input is terminated by a set starting with N = 0. This set should not be processed.
Output
For each test case, output on a line the value of the F(N)%2009.
Sample Input
1
2
3
0
Sample Output
1
7
20
Source
Mean:
f[n]=f[n-2]+3*n*n-3*n+1;
analyse:
本题的循环是4018.
#include <cstdio> #include <cstring> #include <iostream> #include <cmath> #include<vector> #include<queue> #include<algorithm> using namespace std; typedef long long LL; const int maxn=500009; const int INF=0x3f3f3f3f; const int mod=2009; int f[maxn]; void Init() { f[1]=1; f[2]=7; for(int i=3; i<4018; i++) { f[i]=f[i-2]+3*i*i-3*i+1; f[i]%=mod; } } int main() { Init(); int n; while(scanf("%d", &n), n) { printf("%d\n", f[n%4018]); } return 0; }