求助 90pts

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int mod=998244353;
const int N=2e3;
int n,k,x[N],y[N];
int quickly_pow(int a,int p,int mod){
	int tmp=1;
	while(p){
		if(p&1) tmp=tmp*a%mod;
		a=a*a%mod;
		p>>=1;
	} 
	return tmp%mod;
}
int inv(int x){
	return quickly_pow(x,mod-2,mod);
}
signed main(){
	cin>>n>>k;
	for(int i=1;i<=n;i++){
		cin>>x[i]>>y[i];
	}
	int ans=0;
	for(int i=1;i<=n;i++){
		int s1=y[i]%mod,s2=1;
		for(int j=1;j<=n;j++){
			if(i!=j){
				s1=s1*(k-x[j])%mod;
				s2=s2*(x[i]-x[j])%mod;
			}
		}
		ans=(ans+inv(s2)*s1%mod)%mod;
	}
	cout<<(ans+mod)%mod;
	return 0;
}