1 #include<cstdio> 2 #include<cstdlib> 3 #include<cstring> 4 #include<iostream> 5 using namespace std; 6  7 struct node{int s[510];int l;} 8 f[3],c;//1010 9 10 int mmax(int x,int y) {return x>y?x:y;}11 node pplus(node a,node b)12 {13     c.l=mmax(a.l,b.l);14     memset(c.s,0,sizeof(c.s));15     for (int i=1;i<=c.l;i++)16     {17       c.s[i]+=a.s[i]+b.s[i];18       c.s[i+1]+=c.s[i]/10;19       c.s[i]%=10;20     }21     if (c.s[c.l+1]) c.l++;22     return c;23 }24 25 int main()26 {27     int n;28     scanf("%d",&n);29     f[1].l=1,f[1].s[1]=3;30     f[2].l=1,f[2].s[1]=7;31     int u,v,w;32     u=0;33     for (int i=3;i<=n;i++)34     {35       v=(u+2)%3,w=(u+1)%3;//v=(u+3-1)%3,w=(u+3-2)%3;36       f[u]=pplus(pplus(f[v],f[v]),f[w]);37       u=(u+1)%3;38     }//f[i]=pplus(pplus(f[i-1],f[i-1]),f[i-2]);39     int t=(u+2)%3;//(u+3-1)%3;40     if (n<3) t=n;41     for (int i=f[t].l;i>=1;i--)42       printf("%d",f[t].s[i]);43     printf("\n");44     return 0;45 }

 1 #include<cstdio> 2 #include<cstdlib> 3 #include<cstring> 4 #include<iostream> 5 using namespace std; 6  7 int f[3]; 8 int main() 9 {10     int n;11     scanf("%d",&n);12     f[1]=3,  f[2]=7;13     int u,v,w;14     u=0;15     for (int i=3;i<=n;i++)16     {17       v=(u+2)%3,w=(u+1)%3;18       f[u]=(2*f[v]+f[w])%12345;19       u=(u+1)%3;20     }21     if (n<3) printf("%d\n",f[n]);22     else printf("%d\n",f[(u+2)%3]);23     return 0;24 }

 1 #include<cstdio> 2 #include<cstdlib> 3 #include<cstring> 4 #include<iostream> 5 using namespace std; 6  7 long long f[1010]; 8  9 int main()10 {11     int n;12     scanf("%d",&n);13     f[1]=3,  f[2]=7;14     for (int i=3;i<=n;i++)15        f[i]=(2*f[i-1]+f[i-2])%12345;16     printf("%lld\n",f[n]);17     return 0;18 }