提出 #69531647

---

ソースコード 拡げる

#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = std::forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = std::forward<U>(y), true); }

template <class T> void mkuni(std::vector<T>& v) {
    std::ranges::sort(v);
    auto result = std::ranges::unique(v);
    v.erase(result.begin(), result.end());
}

template <class T> int lwb(const std::vector<T>& v, const T& x) {
    return std::distance(v.begin(), std::ranges::lower_bound(v, x));
}

#include <atcoder/modint>

using namespace std;

using ll = long long;

using mint = atcoder::modint998244353;

void solve() {
    int N;
    cin >> N;
    vector<int> A(N);
    for (int i = 0; i < N; i++) {
        cin >> A[i];
        if (A[i] != -1) {
            A[i]--;
        }
    }

    int L = -1, R = -1;
    for (int i = 0; i < N; i++) {
        if (A[i] == -1) {
            continue;
        }
        if (A[i] != i + 1 and A[i] != i - 1) {
            if (L != -1) {
                cout << 0 << "\n";
                return;
            }
            L = min(i, A[i]);
            R = max(i, A[i]);
        }
    }
    auto right = [&](int i) { return A[i] == -1 or A[i] == i + 1; };
    auto left = [&](int i) { return A[i] == -1 or A[i] == i - 1; };
    if (L != -1) {  // 長さ 2 以上のサイクルが既に存在
        for (int i = 0; i < L; i++) {
            if (not right(i)) {
                cout << 0 << "\n";
                return;
            }
        }
        for (int i = R + 1; i < N; i++) {
            if (not left(i)) {
                cout << 0 << "\n";
                return;
            }
        }
        if (A[L] == R) {
            for (int i = L + 1; i <= R; i++) {
                if (not left(i)) {
                    cout << 0 << "\n";
                    return;
                }
            }
        } else {
            assert(A[R] == L);
            for (int i = L; i < R; i++) {
                if (not right(i)) {
                    cout << 0 << "\n";
                    return;
                }
            }
        }
        cout << 1 << "\n";
        return;
    }

    int Right = 0, Left = 0;
    while (Right < N and right(Right)) {
        Right++;
    }
    while (Left < N and left(N - 1 - Left)) {
        Left++;
    }
    mint ans = 0;
    for (int i = 0; i < N; i++) {
        if (Right < i or Left < N - 1 - i) {
            continue;
        }
        if (A[i] == -1) {
            ans += N - (i != 0);
        } else {
            if (A[i] != i - 1) {
                ans++;
            }
        }
    }

    cout << ans.val() << "\n";
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    solve();
    return 0;
}

提出情報

ジャッジ結果