HDU5275 Dylans loves polynomial 拉格朗日插值

#include<bits/stdc++.h>
using namespace std;
const int maxm=3e5+10,mod=1000000007;
const int maxn=4e3+10;
typedef long long ll;

ll fac[maxm],inv[maxm];
ll fpm(ll a,ll b){
    ll ret=1;
    for(;b;b>>=1,a=a*a%mod)
        if(b&1)ret=ret*a%mod;
    return ret;
}
void init(){
    fac[0]=1;
    for(int i=1;i<maxm;++i)
        fac[i]=fac[i-1]*i%mod;
    inv[maxm-1]=fpm(fac[maxm-1],mod-2);
    for(int i=maxm-1;i;--i)
        inv[i-1]=inv[i]*i%mod;
}
ll Inv(ll x){
    ll ret;
    if(x==0)return 0;
    else if(x<0){
        x=-x;
        ret=fac[x-1]*inv[x]%mod;
        ret=mod-ret;
    }else{
        ret=fac[x-1]*inv[x]%mod;
    }
    return ret;
}
int n,x[maxn],y[maxn];
ll f[maxn][maxn];
void input(){
    
    for(int i=1;i<=n;++i){
        scanf("%d%d",x+i,y+i);
        f[0][i]=y[i];
    }
    for(int i=1;i<=n;++i)
        for(int j=1;j+i<=n;++j){
            f[i][j]=(f[i-1][j+1]-f[i-1][j]+mod)%mod;
            f[i][j]=f[i][j]*Inv(x[i+j]-x[j])%mod;
            f[i][j]%=mod;//len i from j
        }
}

ll ans,cur,tmp;
void solve(){
    int m=0;scanf("%d",&m);
    for(int l,r,q;m--;){
        scanf("%d%d%d",&l,&r,&q);
        cur=1;ans=0;
        for(int i=0;i<=r-l;++i){
            (ans+=f[i][l]*cur%mod)%=mod;
            tmp=(q-x[l+i]+mod)%mod;
            cur=cur*tmp%mod;
        }
        printf("%lld
",ans);
        //if(m)puts("");
    }
}
int main(){
    init();
    for(;~scanf("%d",&n);){
        input();
        solve();
    }
    return 0; 
}