拉个狼日插值 亩版题

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#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 = 2005, mod = 998244353;
int n, x[N], y[N], k;
int inv(int x, int b = mod - 2, int ans = 1) {
    for(; b; b >>= 1, x = 1LL * x * x % mod) if(b & 1) ans = 1LL * ans * x % mod;
    return ans;
}
int Lagrange(int n, int *x, int *y, int k) {
    int ans = 0;
    rep(i, 1, n) {
        int s1 = 1, s2 = 1;
        rep(j, 1, n) if(i != j) s1 = 1LL * s1 * (k - x[j] + mod) % mod, s2 = 1LL * s2 * (x[i] - x[j] + mod) % mod;
        ans = (ans + 1LL * y[i] * s1 % mod * inv(s2) % mod) % mod;
    }
    return ans;
}
int main() {
    scanf("%d %d", &n, &k);
    rep(i, 1, n) scanf("%d %d", &x[i], &y[i]);
    return printf("%d
", Lagrange(n, x, y, k)), 0;
}