找规律——[Usaco2005 Jan]Sumsets

暴力枚举下，可以发现规律

#include<stdio.h>
long long a[1000009];
int main()
{
    a[1]=1;
    int n,i,id=1;

    while(scanf("%d",&n)!=EOF)
    {    id=1;
        for(i=2;i<=n;i+=2)
    {
        a[i]=a[i+1]=(a[i-1]+a[id])%1000000000;
        id++;
    }
        printf("%lld\n",a[n]);
    }
    return 0;
}