• 线性递推式(外挂)


    传入前几项,输出低n项的值

     1 #include <cstdio>
     2 #include <cstring>
     3 #include <cmath>
     4 #include <algorithm>
     5 #include <vector>
     6 #include <string>
     7 #include <map>
     8 #include <set>
     9 #include <cassert>
    10 using namespace std;
    11 #define rep(i,a,n) for (int i=a;i<n;i++)
    12 #define per(i,a,n) for (int i=n-1;i>=a;i--)
    13 #define pb push_back
    14 #define mp make_pair
    15 #define all(x) (x).begin(),(x).end()
    16 #define fi first
    17 #define se second
    18 #define SZ(x) ((int)(x).size())
    19 typedef vector<int> VI;
    20 typedef long long ll;
    21 typedef pair<int,int> PII;
    22 const ll mod=1000000007;
    23 ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
    24 // head
    25 
    26 int _,n;
    27 namespace linear_seq {
    28     const int N=10010;
    29     ll res[N],base[N],_c[N],_md[N];
    30 
    31     vector<int> Md;
    32     void mul(ll *a,ll *b,int k) {
    33         rep(i,0,k+k) _c[i]=0;
    34         rep(i,0,k) if (a[i]) rep(j,0,k) _c[i+j]=(_c[i+j]+a[i]*b[j])%mod;
    35         for (int i=k+k-1;i>=k;i--) if (_c[i])
    36             rep(j,0,SZ(Md)) _c[i-k+Md[j]]=(_c[i-k+Md[j]]-_c[i]*_md[Md[j]])%mod;
    37         rep(i,0,k) a[i]=_c[i];
    38     }
    39     int solve(ll n,VI a,VI b) { // a 系数 b 初值 b[n+1]=a[0]*b[n]+...
    40 //        printf("%d
    ",SZ(b));
    41         ll ans=0,pnt=0;
    42         int k=SZ(a);
    43         assert(SZ(a)==SZ(b));
    44         rep(i,0,k) _md[k-1-i]=-a[i];_md[k]=1;
    45         Md.clear();
    46         rep(i,0,k) if (_md[i]!=0) Md.push_back(i);
    47         rep(i,0,k) res[i]=base[i]=0;
    48         res[0]=1;
    49         while ((1ll<<pnt)<=n) pnt++;
    50         for (int p=pnt;p>=0;p--) {
    51             mul(res,res,k);
    52             if ((n>>p)&1) {
    53                 for (int i=k-1;i>=0;i--) res[i+1]=res[i];res[0]=0;
    54                 rep(j,0,SZ(Md)) res[Md[j]]=(res[Md[j]]-res[k]*_md[Md[j]])%mod;
    55             }
    56         }
    57         rep(i,0,k) ans=(ans+res[i]*b[i])%mod;
    58         if (ans<0) ans+=mod;
    59         return ans;
    60     }
    61     VI BM(VI s) {
    62         VI C(1,1),B(1,1);
    63         int L=0,m=1,b=1;
    64         rep(n,0,SZ(s)) {
    65             ll d=0;
    66             rep(i,0,L+1) d=(d+(ll)C[i]*s[n-i])%mod;
    67             if (d==0) ++m;
    68             else if (2*L<=n) {
    69                 VI T=C;
    70                 ll c=mod-d*powmod(b,mod-2)%mod;
    71                 while (SZ(C)<SZ(B)+m) C.pb(0);
    72                 rep(i,0,SZ(B)) C[i+m]=(C[i+m]+c*B[i])%mod;
    73                 L=n+1-L; B=T; b=d; m=1;
    74             } else {
    75                 ll c=mod-d*powmod(b,mod-2)%mod;
    76                 while (SZ(C)<SZ(B)+m) C.pb(0);
    77                 rep(i,0,SZ(B)) C[i+m]=(C[i+m]+c*B[i])%mod;
    78                 ++m;
    79             }
    80         }
    81         return C;
    82     }
    83     int gao(VI a,ll n) {
    84         VI c=BM(a);
    85         c.erase(c.begin());
    86         rep(i,0,SZ(c)) c[i]=(mod-c[i])%mod;
    87         return solve(n,c,VI(a.begin(),a.begin()+SZ(c)));
    88     }
    89 };
    90 
    91 int main(){
    92     //for (scanf("%d",&_);_;_--) {
    93         while(scanf("%d",&n)!=EOF){
    94             printf("%d
    ",linear_seq::gao(VI{1,2,4,7,13,24},n-1));
    95         }
    96     //}
    97 }
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  • 原文地址:https://www.cnblogs.com/yZiii/p/7397738.html
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