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  • 【模板】拉格朗日插值

    传送门:

    #include <cstdio>
    #include <cstring>
    #include <cmath>
    using namespace std;
    #define ll long long
    #define re register
    const int mod=998244353;
    inline void read(int &a)
    {
        a=0;
        int d=1;
        char ch;
        while(ch=getchar(),ch>'9'||ch<'0')
            if(ch=='-')
                d=-1;
        a=ch^48;
        while(ch=getchar(),ch>='0'&&ch<='9')
            a=(a<<3)+(a<<1)+(ch^48);
        a*=d;
    }
    int x[2005],y[2005];
    inline int quickmod(int a,int b)
    {
        int res=1;
        int base=a;
        while(b)
        {
            if(b&1)
                res=1ll*res*base%mod;
            base=1ll*base*base%mod;
            b>>=1;
        }
        return res;
    }
    inline int inv(int x){return quickmod(x,mod-2);}
    int main()
    {
        int n,k;
        read(n);
        read(k);
        for(re int i=1;i<=n;i++)
            read(x[i]),read(y[i]);
        ll ans=0;
        for(re int i=1;i<=n;i++)
        {
            int s1=y[i]%mod;
            int s2=1;
            for(re int j=1;j<=n;j++)
                if(i!=j)
                    s1=1ll*s1*(k-x[j])%mod,s2=1ll*s2*(x[i]-x[j])%mod;
            s1=1ll*s1*inv((s2+mod)%mod)%mod;
            (ans+=s1)%=mod;
            (ans+=mod)%=mod;///不加这句会WA
        }
        printf("%lld",ans);
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/acm1ruoji/p/10909421.html
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