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BM模板求遞推式子

一:題目意思

,求的值,結果對100000007取模。

二:題目思路

令S(n)為所得結果,則S(n)=3S(n-1)-2S(n-2)+S(n-3),不會推。用BM模板,它在給定前10來項的情況下,可以求出線性遞推式的任意項,時間複雜度為O(k2log(n)),k為單次匯入的前幾項數量。

原理看不懂(https://zerol.me/2018/02/06/linearly-recurrent-sequence/)。

三:程式碼+BM模板

#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define
per(i,a,n) for (int i=n-1;i>=a;i--) #define pb push_back #define mp make_pair #define all(x) (x).begin(),(x).end() #define fi first #define se second #define SZ(x) ((int)(x).size()) typedef long long ll; typedef vector<ll> VI; typedef pair<ll,ll> PII; const ll mod=100000007;//注意點 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;} namespace linear_seq { const int N=10010; ll res[N],base[N],_c[N],_md[N]; vector<ll> Md; void mul(ll *a,ll *b,int k) { rep(i,0,k+k) _c[i]=0; rep(i,0,k) if (a[i]) rep(j,0
,k) _c[i+j]=(_c[i+j]+a[i]*b[j])%mod; for (int i=k+k-1;i>=k;i--) if (_c[i]) rep(j,0,SZ(Md)) _c[i-k+Md[j]]=(_c[i-k+Md[j]]-_c[i]*_md[Md[j]])%mod; rep(i,0,k) a[i]=_c[i]; } ll solve(ll n,VI a,VI b) { ll ans=0,pnt=0; int k=SZ(a); assert(SZ(a)==SZ(b)); rep(i,0,k) _md[k-1-i]=-a[i];_md[k]=1; Md.clear(); rep(i,0,k) if (_md[i]!=0) Md.push_back(i); rep(i,0,k) res[i]=base[i]=0; res[0]=1; while ((1ll<<pnt)<=n) pnt++; for (int p=pnt;p>=0;p--) { mul(res,res,k); if ((n>>p)&1) { for (int i=k-1;i>=0;i--) res[i+1]=res[i];res[0]=0; rep(j,0,SZ(Md)) res[Md[j]]=(res[Md[j]]-res[k]*_md[Md[j]])%mod; } } rep(i,0,k) ans=(ans+res[i]*b[i])%mod; if (ans<0) ans+=mod; return ans; } VI BM(VI s) { VI C(1,1),B(1,1); int L=0,m=1,b=1; rep(n,0,SZ(s)) { ll d=0; rep(i,0,L+1) d=(d+(ll)C[i]*s[n-i])%mod; if (d==0) ++m; else if (2*L<=n) { VI T=C; ll c=mod-d*powmod(b,mod-2)%mod; while (SZ(C)<SZ(B)+m) C.pb(0); rep(i,0,SZ(B)) C[i+m]=(C[i+m]+c*B[i])%mod; L=n+1-L; B=T; b=d; m=1; } else { ll c=mod-d*powmod(b,mod-2)%mod; while (SZ(C)<SZ(B)+m) C.pb(0); rep(i,0,SZ(B)) C[i+m]=(C[i+m]+c*B[i])%mod; ++m; } } return C; } ll gao(VI a,ll n) { VI c=BM(a); c.erase(c.begin()); rep(i,0,SZ(c)) c[i]=(mod-c[i])%mod; return solve(n,c,VI(a.begin(),a.begin()+SZ(c))); } }; const int MAXN=1e6+5; ll a[MAXN]; ll qk(ll x,ll y){ ll ans=1; while(y){ if(y&1) ans=(ans*x)%mod; y>>=1; x=(x*x)%mod; } return ans; } ll inv(ll x){ return qk(x,mod-2); } ll C(ll n,ll m){ return a[n]*(inv(a[m]*a[n-m]%mod))%mod; } ll T(int x,int y){ return C(x+y*2+2,x-y); } int main() { vector<ll>v,vv; a[0]=1; for(int i=1;i<MAXN;i++) a[i]=(a[i-1]*i)%mod; for(int i=0;i<=15;i++){ int k=i/2;ll t=0; for(int j=0;j<=k;j++){ t+=T(i-j,j); t%=mod; } v.push_back(t); } int nCase,n; scanf("%d", &nCase); while(nCase--){ vv=v; scanf("%d",&n); printf("%lld\n",linear_seq::gao(vv,n)%mod); } }
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