Submission #781203

#	Time	Username	Problem	Language	Result	Execution time	Memory
781203		skittles1412	Linear Garden (IOI08_linear_garden)	C++17	100 / 100	386 ms	25900 KiB

linear_garden

#include "bits/extc++.h"

using namespace std;

template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
    cerr << t;
    ((cerr << " | " << u), ...);
    cerr << endl;
}

#ifdef DEBUG
#define dbg(...)                                           \
    cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
         << ": ";                                          \
    dbgh(__VA_ARGS__)
#else
#define cerr   \
    if (false) \
    cerr
#define dbg(...)
#endif

using i8 = int8_t;

#define endl "\n"
#define long int64_t
#define sz(x) int(std::size(x))

int MOD;

struct mint {
    static int norm(long x) {
        x %= MOD;
        if (x < 0) {
            x += MOD;
        }
        return int(x);
    }

    int x;

    mint() : x(0) {}
    mint(long x) : x(norm(x)) {}

    static mint from_unchecked(int x) {
        mint m;
        m.x = x;
        return m;
    }

    friend ostream& operator<<(ostream& out, const mint& m) {
        return out << m.x;
    }

    mint operator-() const {
        if (!x) {
            return {};
        } else {
            return mint::from_unchecked(MOD - x);
        }
    }

    mint& operator+=(const mint& m) {
        x += m.x;
        if (x >= MOD) {
            x -= MOD;
        }
        return *this;
    }
    mint& operator-=(const mint& m) {
        return *this += -m;
    }

    mint& operator*=(const mint& m) {
        x = int(long(x) * m.x % MOD);
        return *this;
    }

    friend mint operator+(mint a, const mint& b) {
        return a += b;
    }
    friend mint operator-(mint a, const mint& b) {
        return a -= b;
    }
    friend mint operator*(mint a, const mint& b) {
        return a *= b;
    }
};

struct Solver {
    int n, ql, qr;
    const vector<i8>& arr;
    vector<array<mint, 6>> memo;

    Solver(const vector<i8>& arr, int ql, int qr)
        : n(sz(arr)), arr(arr), ql(ql), qr(qr), memo(n) {
        for (auto& a : memo) {
            a.fill(mint::from_unchecked(-1));
        }
    }

    mint dp(int ind, int psum, bool lt) {
        if (!(ql <= psum && psum <= qr)) {
            return 0;
        } else if (ind == n) {
            return lt;
        }

        mint& ans = memo[ind][(psum - ql) * 2 + lt];
        if (ans.x != -1) {
            return ans;
        }

        ans = 0;

        for (int x : {-1, +1}) {
            if (!lt && x > arr[ind]) {
                continue;
            }

            ans += dp(ind + 1, psum + x, lt || (x < arr[ind]));
        }

        return ans;
    }

    mint solve() {
        auto id = [&](int psum, bool lt) -> int {
            return (psum - ql) * 2 + lt;
        };

        array<mint, 6> memo;

        for (int psum = ql; psum <= qr; psum++) {
            for (bool lt : {false, true}) {
                memo[id(psum,lt)] = lt;
            }
        }

        for (int i = n - 1; i >= 0; i--) {
            array<mint, 6> n_memo;

            for (int psum = ql; psum <= qr; psum++) {
                for (bool lt : {false, true}) {
                    mint& ans = n_memo[id(psum, lt)];

                    ans = 0;

                    for (int x : {-1, +1}) {
                        if (!lt && x > arr[i]) {
                            continue;
                        }

                        ans += dp(i + 1, psum + x, lt || (x < arr[i]));
                    }
                }
            }

            memo = n_memo;
        }

        return memo[id(0, false)];
    }
};

void solve() {
    int n;
    cin >> n >> MOD;

    vector<i8> arr(n);
    {
        string s;
        cin >> s;
        for (int i = 0; i < n; i++) {
            if (s[i] == 'L') {
                arr[i] = -1;
            } else {
                assert(s[i] == 'P');
                arr[i] = +1;
            }
        }
    }

    auto solve = [&](int ql, int qr) -> mint {
        return Solver(arr, ql, qr).solve();
    };

    cout << solve(-2, 0) + solve(-1, 1) + solve(0, 2) - solve(-1, 0) -
                solve(0, 1) + 1
         << endl;
}

int main() {
    cin.tie(nullptr);
    cin.exceptions(ios::failbit);
    ios_base::sync_with_stdio(false);
    solve();
}

Compilation message (stderr)

linear_garden.cpp: In constructor 'Solver::Solver(const std::vector<signed char>&, int, int)':
linear_garden.cpp:93:23: warning: 'Solver::arr' will be initialized after [-Wreorder]
   93 |     const vector<i8>& arr;
      |                       ^~~
linear_garden.cpp:92:12: warning:   'int Solver::ql' [-Wreorder]
   92 |     int n, ql, qr;
      |            ^~
linear_garden.cpp:96:5: warning:   when initialized here [-Wreorder]
   96 |     Solver(const vector<i8>& arr, int ql, int qr)
      |     ^~~~~~

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