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  • 多项式乘法逆元

    递归求解即可

    #include <bits/stdc++.h>
    using namespace std;
    #define int long long
    namespace NTT {
        #define pw(n) (1<<n)
        const int N=4000005; // 4 times!
        const int mod=998244353,g=3;
        int n,m,bit,bitnum,a[N+5],b[N+5],rev[N+5];
        void getrev(int l){
            for(int i=0;i<pw(l);i++){
                rev[i]=(rev[i>>1]>>1)|((i&1)<<(l-1));
            }
        }
        int fastpow(int a,int b){
            int ans=1;
            for(;b;b>>=1,a=1LL*a*a%mod){
                if(b&1)ans=1LL*ans*a%mod;
            }
            return ans;
        }
        void NTT(int *s,int op){
            for(int i=0;i<bit;i++)if(i<rev[i])swap(s[i],s[rev[i]]);
            for(int i=1;i<bit;i<<=1){
                int w=fastpow(g,(mod-1)/(i<<1));
                for(int p=i<<1,j=0;j<bit;j+=p){
                    int wk=1;
                    for(int k=j;k<i+j;k++,wk=1LL*wk*w%mod){
                        int x=s[k],y=1LL*s[k+i]*wk%mod;
                        s[k]=(x+y)%mod;
                        s[k+i]=(x-y+mod)%mod;
                    }
                }
            }
            if(op==-1){
                reverse(s+1,s+bit);
                int inv=fastpow(bit,mod-2);
                for(int i=0;i<bit;i++)a[i]=1LL*a[i]*inv%mod;
            }
        }
        void solve(vector <int> A,vector <int> B,vector <int> &C) {
            n=A.size()-1;
            m=B.size()-1;
            for(int i=0;i<=n;i++) a[i]=A[i];
            for(int i=0;i<=m;i++) b[i]=B[i];
            m+=n;
            bitnum=0;
            for(bit=1;bit<=m;bit<<=1)bitnum++;
            getrev(bitnum);
            NTT(a,1);
            NTT(b,1);
            for(int i=0;i<bit;i++)a[i]=1LL*a[i]*b[i]%mod;
            NTT(a,-1);
            C.clear();
            for(int i=0;i<=m;i++) C.push_back(a[i]);
            for(int i=0;i<=min(m*2,N-1);i++) a[i]=b[i]=0;
        }
    }
    
    const int N=4000005; // 4 times!
    const int mod=998244353,g=3;
    
    struct poly {
        vector <int> a;
        void cut(int n) {
            while(a.size()>n) a.pop_back();
        }
        poly operator *(int b) {
            poly c=*this;
            for(int i=0;i<a.size();i++) (((c.a[i]*=b)%=mod)+=mod)%=mod;
            return c;
        }
        poly operator *(const poly &b) {
            poly c;
            NTT::solve(a,b.a,c.a);
            return c;
        }
        poly operator +(poly b) {
            int len=max(a.size(),b.a.size());
            a.resize(len);
            b.a.resize(len);
            poly c;
            for(int i=0;i<len;i++) c.a.push_back((a[i]+b.a[i])%mod);
            return c;
        }
        poly operator -(poly b) {
            int len=max(a.size(),b.a.size());
            a.resize(len);
            b.a.resize(len);
            poly c;
            for(int i=0;i<len;i++) c.a.push_back(((a[i]-b.a[i])%mod+mod)%mod);
            return c;
        }
    };
    
    void print(poly x) {
        for(int i=0;i<x.a.size();i++) cout<<x.a[i]<<" ";
        cout<<endl;
    }
    
    int n,a[N];
    
    int qpow(int p,int q) {
        int r = 1;
        for(; q; p*=p, p%=mod, q>>=1) if(q&1) r*=p, r%=mod;
        return r;
    }
    
    int inv(int p) {
        return qpow(p, mod-2);
    }
    
    poly solve(poly A, int n) {
        A.cut(n);
        poly B;
        if(n==1) {
            B.a.push_back(inv(A.a[0]));
        }
        else {
    
            poly Bi = solve(A,(n-1)/2+1);
            B = Bi*2 - A*Bi*Bi;
            B.cut(n);
        }
        return B;
    }
    
    signed main() {
        ios::sync_with_stdio(false);
        cin>>n;
        for(int i=0;i<n;i++) cin>>a[i];
        poly A;
        for(int i=0;i<n;i++) A.a.push_back(a[i]);
        poly B = solve(A,n);
        print(B);
    }
    
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  • 原文地址:https://www.cnblogs.com/mollnn/p/12316143.html
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