拉个狼日插值 亩版题

#include <iostream>
#include <cstdio>
#include <fstream>
#include <algorithm>
#include <cmath>
#include <deque>
#include <vector>
#include <queue>
#include <string>
#include <cstring>
#include <map>
#include <stack>
#include <set>
#define LL long long
#define ULL unsigned long long
#define rep(i,j,k) for(int i=j;i<=k;i++)
#define dep(i,j,k) for(int i=k;i>=j;i--)
#define INF 0x3f3f3f3f
#define mem(i,j) memset(i,j,sizeof(i))
#define make(i,j) make_pair(i,j)
#define pb push_back
#define Pi acos(-1.0)
using namespace std;
const int N = 2e3 + 5, mod = 998244353;
int x[N], y[N];
int ksm(int a, int b) {
    int ans = 1;
    while(b) {
        if(b & 1) ans = 1LL * ans * a % mod;
        a = 1LL * a * a % mod;
        b >>= 1;
    }
    return ans;
}
int inv(int a) {
    return ksm(a, mod - 2);
}
int main() {
    int n, k;
    scanf("%d %d", &n, &k);
    rep(i, 1, n) scanf("%d %d", &x[i], &y[i]);
    LL ans = 0;
    rep(i, 1, n) {
        int s1 = y[i] % mod, s2 = 1;
        rep(j, 1, n) {
            if(i == j) continue;
            s1 = 1LL * (k - x[j]) * s1 % mod;
            s2 = 1LL * s2 * (x[i] - x[j]) % mod;
        }
        s1 = 1LL * s1 * inv((s2 + mod) % mod) % mod;
        ans = (ans + s1 + mod) % mod;
    }
    cout << ans << endl;
    return 0;
}