学过高数的话，是不是应该知道拉格朗日插值？

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 0x3f3f3f3f3f3f3f3f;
typedef multiset<ll>::iterator itt;
const int N = 2e3+11, P = 998244353;

ll n, k, x[N], y[N];

ll ksm(ll a, ll b){
	ll x = 1;
	while(b){
		if(b & 1) x = x * a % P;
		a = a * a % P; b >>= 1;
	} return x;
}

void work(){
	scanf("%lld%lld",&n,&k);
	for(int i=0;i<n;i++) scanf("%lld%lld",&x[i],&y[i]);
	
	ll ans = 0;
	for(int i=0;i<n;i++){
		ll a = y[i], b = 1;
		for(int j=0;j<n;j++) if(j != i){
			a = a * (k - x[j] + P) % P;
			b = b * (x[i] - x[j] + P) % P;		
		} ans = ans + (a * ksm(b, P - 2)) % P;
	} printf("%lld\n",(ans + P) % P);
}

int main(){
	int t = 1; // scanf("%d",&t);
	while(t--) work(); return 0;
}