Submission #28865352

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Source Code Expand

#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define trav(u, x) for (auto &u : x)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

using namespace atcoder;
using mint = modint998244353;

void solve() {
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n);

    rep(i, 0, n) cin >> a[i];
    rep(i, 1, n) a[0] -= a[i];
    if(a[0]<k) {
        cout << "0\n";
        return;
    }

    mint inv = 1;
    rep(i, 1, k) inv *= mint(i).inv();

    auto binom = [&](mint n) {
        mint res = inv;
        rep(i, 0, k-1) res *= n-i;
        return res;
    };

    mint res = binom(a[0]-1);
    rep(i, 1, n) res *= binom(a[i]+k-1);
    cout << res.val() << "\n"; 
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    solve();
}

Submission Info

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