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  • edu9E. Thief in a Shop

    题意:n个物品每个价值a[i],要求选k个,可以重复,问能取到哪几个价值
    题解:fft裸题.但是直接一次fft,然后快速幂会boom.这样是严格的(2^{20}*log2(2^{20})*log(w)).需要在快速幂里fft,每次取最大的2的次幂,然后fft也boom了,不知道是不是写搓了.ntt过了.....

    //#pragma GCC optimize(2)
    //#pragma GCC optimize(3)
    //#pragma GCC optimize(4)
    //#pragma GCC optimize("unroll-loops")
    //#pragma comment(linker, "/stack:200000000")
    //#pragma GCC optimize("Ofast,no-stack-protector")
    //#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
    #include<bits/stdc++.h>
    #define fi first
    #define se second
    #define db double
    #define mp make_pair
    #define pb push_back
    #define pi acos(-1.0)
    #define ll long long
    #define vi vector<int>
    #define mod 998244353
    #define ld long double
    //#define C 0.5772156649
    //#define ls l,m,rt<<1
    //#define rs m+1,r,rt<<1|1
    #define pll pair<ll,ll>
    #define pil pair<int,ll>
    #define pli pair<ll,int>
    #define pii pair<int,int>
    #define ull unsigned long long
    //#define base 1000000000000000000
    #define fin freopen("a.txt","r",stdin)
    #define fout freopen("a.txt","w",stdout)
    #define fio ios::sync_with_stdio(false);cin.tie(0)
    inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
    inline void sub(ll &a,ll b){a-=b;if(a<0)a+=mod;}
    inline void add(ll &a,ll b){a+=b;if(a>=mod)a-=mod;}
    template<typename T>inline T const& MAX(T const &a,T const &b){return a>b?a:b;}
    template<typename T>inline T const& MIN(T const &a,T const &b){return a<b?a:b;}
    inline ll qp(ll a,ll b){ll ans=1;while(b){if(b&1)ans=ans*a%mod;a=a*a%mod,b>>=1;}return ans;}
    inline ll qp(ll a,ll b,ll c){ll ans=1;while(b){if(b&1)ans=ans*a%c;a=a*a%c,b>>=1;}return ans;}
    
    using namespace std;
    
    const ull ba=233;
    const db eps=1e-5;
    const ll INF=0x3f3f3f3f3f3f3f3f;
    const int N=1000000+10,maxn=1000000+10,inf=0x3f3f3f3f;
    
    ll x[N<<3],y[N<<3];
    int rev[N<<3];
    void getrev(int bit)
    {
        for(int i=0;i<(1<<bit);i++)
            rev[i]=(rev[i>>1]>>1) | ((i&1)<<(bit-1));
    }
    void ntt(ll *a,int n,int dft)
    {
        for(int i=0;i<n;i++)
            if(i<rev[i])
                swap(a[i],a[rev[i]]);
        for(int step=1;step<n;step<<=1)
        {
            ll wn=qp(3,(mod-1)/(step*2));
            if(dft==-1)wn=qp(wn,mod-2);
            for(int j=0;j<n;j+=step<<1)
            {
                ll wnk=1;
                for(int k=j;k<j+step;k++)
                {
                    ll x=a[k];
                    ll y=wnk*a[k+step]%mod;
                    a[k]=(x+y)%mod;a[k+step]=(x-y+mod)%mod;
                    wnk=wnk*wn%mod;
                }
            }
        }
        if(dft==-1)
        {
            ll inv=qp(n,mod-2);
            for(int i=0;i<n;i++)a[i]=a[i]*inv%mod;
        }
    }
    void solve(int k,int p)
    {
        int sz=0;while((1<<sz)<=p)sz++;sz++;
        getrev(sz);
        ntt(y,(1<<sz),1);
        if(k&1)
        {
            ntt(x,(1<<sz),1);
            for(int i=0;i<(1<<sz);i++)x[i]=x[i]*y[i]%mod;
            ntt(x,(1<<sz),-1);
            for(int i=0;i<(1<<sz);i++)if(x[i])x[i]=1;
        }
        for(int i=0;i<(1<<sz);i++)y[i]=y[i]*y[i]%mod;
        ntt(y,(1<<sz),-1);
        for(int i=0;i<(1<<sz);i++)if(y[i])y[i]=1;
    }
    int main()
    {
        int n,k,ma=0;scanf("%d%d",&n,&k);
        for(int i=1;i<=n;i++)
        {
            int a;scanf("%d",&a);
            y[a]+=1;ma=max(ma,a);
        }
        x[0]=1;
        while(k)solve(k,ma),k>>=1,ma<<=1;
        for(int i=1;i<N;i++)if(x[i]!=0)printf("%d ",i);
        return 0;
    }
    /********************
    
    ********************/
    
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  • 原文地址:https://www.cnblogs.com/acjiumeng/p/10752820.html
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