結果

問題 No.1740 Alone 'a'
コンテスト
ユーザー Forested
提出日時 2021-11-12 21:48:02
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 51 ms / 2,000 ms
コード長 7,238 bytes
コンパイル時間 1,099 ms
コンパイル使用メモリ 116,832 KB
最終ジャッジ日時 2025-01-25 16:22:34
ジャッジサーバーID
（参考情報） 		judge3 / judge1
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ファイルパターン 結果
sample AC * 3
other AC * 38
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#define OVERRIDE(a, b, c, d, ...) d
#define REP2(i, n) for (i32 i = 0; i < (n); ++i)
#define REP3(i, m, n) for (i32 i = (m); i < (n); ++i)
#define REP(...) OVERRIDE(__VA_ARGS__, REP3, REP2)(__VA_ARGS__)
#define PER(i, n) for (i32 i = (n) - 1; i >= 0; --i)
#define ALL(x) begin(x), end(x)

using namespace std;

using u32 = unsigned int;
using u64 = unsigned long long;
using u128 = __uint128_t;
using i32 = signed int;
using i64 = signed long long;
using i128 = __int128_t;

template <typename T>
using Vec = vector<T>;

template <typename T>
bool chmin(T &x, const T &y) {
    if (x > y) {
        x = y;
        return true;
    }
    return false;
}
template <typename T>
bool chmax(T &x, const T &y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}

[[maybe_unused]] constexpr i32 inf = 1000000100;
[[maybe_unused]] constexpr i64 inf64 = 3000000000000000100;

struct SetIO {
    SetIO() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(10);
    }
} set_io;

// ----- "mod_int.hpp" -----
#ifndef MOD_INT_HPP
#define MOD_INT_HPP

#include <cassert>
#include <type_traits>
#include <iostream>

// ----- "utils.hpp" -----
#ifndef UTILS_HPP
#define UTILS_HPP

#include <cstddef>
 
 
constexpr bool is_prime(unsigned n) {
    if (n == 0 || n == 1)
        return false;
    for (unsigned i = 2; i * i <= n; ++i) {
        if (n % i == 0)
            return false;
    }
    return true;
}
 
constexpr unsigned mod_pow(unsigned x, unsigned y, unsigned mod) {
    unsigned ret = 1, self = x;
    while (y != 0) {
        if (y & 1)
            ret = (unsigned long long) ret * self % mod;
        self = (unsigned long long) self * self % mod;
        y >>= 1;
    }
    return ret;
}
 
template <unsigned mod>
constexpr unsigned primitive_root() {
    static_assert(is_prime(mod), "`mod` must be a prime number.");
    if (mod == 2)
        return 1;
    
    unsigned primes[32] = {};
    std::size_t it = 0;
    {
        unsigned m = mod - 1;
        for (unsigned i = 2; i * i <= m; ++i) {
            if (m % i == 0) {
                primes[it++] = i;
                while (m % i == 0)
                    m /= i;
            }
        }
        if (m != 1)
            primes[it++] = m;
    }
    for (unsigned i = 2; i < mod; ++i) {
        bool ok = true;
        for (std::size_t j = 0; j < it; ++j) {
            if (mod_pow(i, (mod - 1) / primes[j], mod) == 1) {
                ok = false;
                break;
            }
        }
        if (ok)
            return i;
    }
    return 0;
}

#endif
// ----- "utils.hpp" -----

template <typename T, std::enable_if_t<std::is_signed_v<T>> * = nullptr>
constexpr unsigned safe_mod(T x, unsigned mod) {
    if (x < 0) {
        return (unsigned) (x % mod + mod);
    } else {
        return (unsigned) (x % mod);
    }
}

template <typename T, std::enable_if_t<std::is_unsigned_v<T>> * = nullptr>
constexpr unsigned safe_mod(T x, unsigned mod) {
    return (unsigned) (x % mod);
}

template <unsigned mod> class ModInt {
    static_assert(mod != 0, "`mod` must not be equal to 0.");
    static_assert(mod < (1u << 31), "`mod` must be less than (1u << 31) = 2147483648.");
    
    unsigned val;
    
public:
    constexpr ModInt() : val(0) {}
    template <typename T> constexpr ModInt(T x) : val(safe_mod(x, mod)) {}
    
    static constexpr ModInt raw(unsigned x) {
        ModInt<mod> ret;
        ret.val = x;
        return ret;
    }
    
    constexpr unsigned get_val() const {
        return val;
    }
    
    constexpr ModInt operator+() const {
        return *this;
    }
    constexpr ModInt operator-() const {
        return ModInt<mod>(0u) - *this;
    }
    
    constexpr ModInt &operator+=(const ModInt &rhs) {
        val += rhs.val;
        if (val >= mod)
            val -= mod;
        return *this;
    }
    constexpr ModInt &operator-=(const ModInt &rhs) {
        if (val < rhs.val)
            val += mod;
        val -= rhs.val;
        return *this;
    }
    constexpr ModInt &operator*=(const ModInt &rhs) {
        val = (unsigned long long) val * rhs.val % mod;
        return *this;
    }
    constexpr ModInt &operator/=(const ModInt &rhs) {
        val = (unsigned long long) val * rhs.inv().val % mod;
        return *this;
    }
    
    friend constexpr ModInt operator+(const ModInt &lhs, const ModInt &rhs) {
        return ModInt<mod>(lhs) += rhs;
    }
    friend constexpr ModInt operator-(const ModInt &lhs, const ModInt &rhs) {
        return ModInt<mod>(lhs) -= rhs;
    }
    friend constexpr ModInt operator*(const ModInt &lhs, const ModInt &rhs) {
        return ModInt<mod>(lhs) *= rhs;
    }
    friend constexpr ModInt operator/(const ModInt &lhs, const ModInt &rhs) {
        return ModInt<mod>(lhs) /= rhs;
    }
    
    constexpr ModInt pow(unsigned x) const {
        ModInt<mod> ret = ModInt<mod>::raw(1);
        ModInt<mod> self = *this;
        while (x != 0) {
            if (x & 1)
                ret *= self;
            self *= self;
            x >>= 1;
        }
        return ret;
    }
    constexpr ModInt inv() const {
        static_assert(is_prime(mod), "`mod` must be a prime number.");
        assert(val != 0);
        return this->pow(mod - 2);
    }
    
    friend std::istream &operator>>(std::istream &is, ModInt<mod> &x) {
        is >> x.val;
        // x.val %= mod;
        return is;
    }
    
    friend std::ostream &operator<<(std::ostream &os, const ModInt<mod> &x) {
        os << x.val;
        return os;
    }
    
    friend bool operator==(const ModInt &lhs, const ModInt &rhs) {
        return lhs.val == rhs.val;
    }
};

[[maybe_unused]] constexpr unsigned mod998244353 = 998244353;
[[maybe_unused]] constexpr unsigned mod1000000007 = 1000000007;

#endif
// ----- "mod_int.hpp" -----

using Mint = ModInt<mod998244353>;

int main() {
    i32 n;
    cin >> n;
    string s;
    cin >> s;
    
    Vec<Mint> dp_ns_na(n + 1), dp_ns_a(n + 1), dp_s_na(n + 1), dp_s_a(n + 1);
    dp_ns_na[0] = Mint(1);
    REP(i, n) {
        for (char c = 'a'; c <= 'z'; ++c) {
            if (c == 'a') {
                dp_s_a[i + 1] += dp_s_na[i];
            } else {
                dp_s_na[i + 1] += dp_s_na[i];
                dp_s_a[i + 1] += dp_s_a[i];
            }
            if (c < s[i]) {
                if (c == 'a') {
                    dp_s_a[i + 1] += dp_ns_na[i];
                } else {
                    dp_s_na[i + 1] += dp_ns_na[i];
                    dp_s_a[i + 1] += dp_ns_a[i];
                }
            }
            if (c == s[i]) {
                if (c == 'a') {
                    dp_ns_a[i + 1] += dp_ns_na[i];
                } else {
                    dp_ns_na[i + 1] += dp_ns_na[i];
                    dp_ns_a[i + 1] += dp_ns_a[i];
                }
            }
        }
    }
    cout << dp_s_a[n] << '\n';
}
0