Submission #891961

#	Time	Username	Problem	Language	Result	Execution time	Memory
891961		josanneo22	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	6 ms	476 KiB

kangaroo

#include<bits/stdc++.h>
using namespace std;
using i64 = long long;

char buf[1 << 23], * p1 = buf, * p2 = buf;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
template<typename T> inline void re(T& x) { x = 0; T f = 1; char ch = getchar();  while (!isdigit(ch)) { if (ch == '-') f = -1; ch = getchar(); } while (isdigit(ch)) { x = x * (1 << 1) + x * (1 << 3) + (ch - 48); ch = getchar(); } x *= f; }
template<typename x, typename... y>void re(x& a, y&... b) { re(a); re(b...); }
template<typename T> inline void ps(T x) { if (x < 0) { putchar('-'); x = -x; } if (x > 9)  ps(x / 10); putchar(x % 10 + '0'); }
template<typename x, typename... y>void ps(x& a, y&... b) { ps(a); putchar(' '); ps(b...); }
#define sp putchar(' ')
#define nl putchar('\n')

template<class T>
constexpr T power(T a, i64 b) {
    T res = 1;
    for (; b; b /= 2, a *= a) {
        if (b % 2) {
            res *= a;
        }
    }
    return res;
}

constexpr i64 mul(i64 a, i64 b, i64 p) {
    i64 res = a * b - i64(1.L * a * b / p) * p;
    res %= p;
    if (res < 0) {
        res += p;
    }
    return res;
}
template<i64 P>
struct MLong {
    i64 x;
    constexpr MLong() : x{} {}
    constexpr MLong(i64 x) : x{ norm(x % getMod()) } {}

    static i64 Mod;
    constexpr static i64 getMod() {
        if (P > 0) {
            return P;
        }
        else {
            return Mod;
        }
    }
    constexpr static void setMod(i64 Mod_) {
        Mod = Mod_;
    }
    constexpr i64 norm(i64 x) const {
        if (x < 0) {
            x += getMod();
        }
        if (x >= getMod()) {
            x -= getMod();
        }
        return x;
    }
    constexpr i64 val() const {
        return x;
    }
    explicit constexpr operator i64() const {
        return x;
    }
    constexpr MLong operator-() const {
        MLong res;
        res.x = norm(getMod() - x);
        return res;
    }
    constexpr MLong inv() const {
        assert(x != 0);
        return power(*this, getMod() - 2);
    }
    constexpr MLong& operator*=(MLong rhs)& {
        x = mul(x, rhs.x, getMod());
        return *this;
    }
    constexpr MLong& operator+=(MLong rhs)& {
        x = norm(x + rhs.x);
        return *this;
    }
    constexpr MLong& operator-=(MLong rhs)& {
        x = norm(x - rhs.x);
        return *this;
    }
    constexpr MLong& operator/=(MLong rhs)& {
        return *this *= rhs.inv();
    }
    friend constexpr MLong operator*(MLong lhs, MLong rhs) {
        MLong res = lhs;
        res *= rhs;
        return res;
    }
    friend constexpr MLong operator+(MLong lhs, MLong rhs) {
        MLong res = lhs;
        res += rhs;
        return res;
    }
    friend constexpr MLong operator-(MLong lhs, MLong rhs) {
        MLong res = lhs;
        res -= rhs;
        return res;
    }
    friend constexpr MLong operator/(MLong lhs, MLong rhs) {
        MLong res = lhs;
        res /= rhs;
        return res;
    }
    friend constexpr std::istream& operator>>(std::istream& is, MLong& a) {
        i64 v;
        is >> v;
        a = MLong(v);
        return is;
    }
    friend constexpr std::ostream& operator<<(std::ostream& os, const MLong& a) {
        return os << a.val();
    }
    friend constexpr bool operator==(MLong lhs, MLong rhs) {
        return lhs.val() == rhs.val();
    }
    friend constexpr bool operator!=(MLong lhs, MLong rhs) {
        return lhs.val() != rhs.val();
    }
};

template<>
i64 MLong<0LL>::Mod = i64(1E18) + 9;

template<int P>
struct MInt {
    int x;
    constexpr MInt() : x{} {}
    constexpr MInt(i64 x) : x{ norm(x % getMod()) } {}

    static int Mod;
    constexpr static int getMod() {
        if (P > 0) {
            return P;
        }
        else {
            return Mod;
        }
    }
    constexpr static void setMod(int Mod_) {
        Mod = Mod_;
    }
    constexpr int norm(int x) const {
        if (x < 0) {
            x += getMod();
        }
        if (x >= getMod()) {
            x -= getMod();
        }
        return x;
    }
    constexpr int val() const {
        return x;
    }
    explicit constexpr operator int() const {
        return x;
    }
    constexpr MInt operator-() const {
        MInt res;
        res.x = norm(getMod() - x);
        return res;
    }
    constexpr MInt inv() const {
        assert(x != 0);
        return power(*this, getMod() - 2);
    }
    constexpr MInt& operator*=(MInt rhs)& {
        x = 1LL * x * rhs.x % getMod();
        return *this;
    }
    constexpr MInt& operator+=(MInt rhs)& {
        x = norm(x + rhs.x);
        return *this;
    }
    constexpr MInt& operator-=(MInt rhs)& {
        x = norm(x - rhs.x);
        return *this;
    }
    constexpr MInt& operator/=(MInt rhs)& {
        return *this *= rhs.inv();
    }
    friend constexpr MInt operator*(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res *= rhs;
        return res;
    }
    friend constexpr MInt operator+(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res += rhs;
        return res;
    }
    friend constexpr MInt operator-(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res -= rhs;
        return res;
    }
    friend constexpr MInt operator/(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res /= rhs;
        return res;
    }
    friend constexpr std::istream& operator>>(std::istream& is, MInt& a) {
        i64 v;
        is >> v;
        a = MInt(v);
        return is;
    }
    friend constexpr std::ostream& operator<<(std::ostream& os, const MInt& a) {
        return os << a.val();
    }
    friend constexpr bool operator==(MInt lhs, MInt rhs) {
        return lhs.val() == rhs.val();
    }
    friend constexpr bool operator!=(MInt lhs, MInt rhs) {
        return lhs.val() != rhs.val();
    }
};

template<>
int MInt<0>::Mod = 1E9 + 7;

template<int V, int P>
constexpr MInt<P> CInv = MInt<P>(V).inv();

constexpr int P = 1E9 + 7;
using Z = MInt<P>;

struct Comb {
    int n;
    std::vector<Z> _fac;
    std::vector<Z> _invfac;
    std::vector<Z> _inv;

    Comb() : n{ 0 }, _fac{ 1 }, _invfac{ 1 }, _inv{ 0 } {}
    Comb(int n) : Comb() {
        init(n);
    }

    void init(int m) {
        m = std::min(m, Z::getMod() - 1);
        if (m <= n) return;
        _fac.resize(m + 1);
        _invfac.resize(m + 1);
        _inv.resize(m + 1);

        for (int i = n + 1; i <= m; i++) {
            _fac[i] = _fac[i - 1] * i;
        }
        _invfac[m] = _fac[m].inv();
        for (int i = m; i > n; i--) {
            _invfac[i - 1] = _invfac[i] * i;
            _inv[i] = _invfac[i] * _fac[i - 1];
        }
        n = m;
    }
    Z fac(int m) {
        if (m > n) init(2 * m);
        return _fac[m];
    }
    Z invfac(int m) {
        if (m > n) init(2 * m);
        return _invfac[m];
    }
    Z inv(int m) {
        if (m > n) init(2 * m);
        return _inv[m];
    }
    Z C(int n, int m) {
        if (n < m || m < 0) return 0;
        return fac(n) * invfac(m) * invfac(n - m);
    }
    Z find(int n, int m, int k) {
        /*  x1+x2+x3+...+xm = k and 0<=x1,x2,x3...,xm<n
            x1+x2+x3+...=k+m and x1,x2,x3...xm>=1
            f(i) = no of cases such that >=i numbers are >n
            f(i) = m C i * (m+k-i*n-1) C (m-1)
            ans= f(i) * (-1)^i for i->[0,m] */
        Z ans = 0; int ops = 1;
        for (int i = 0; i <= m; i++) {
            Z t = C(m, i) * C(m + k - i * n - 1, m - 1);
            if (ops == -1) ans -= t;
            else ans += t;
            ops *= -1;
        }
        return ans;
    }

} comb;

//mod = 1E9+7

const int _N = 2010;
Z dp[2][_N];
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);

    int N, A, B; re(N, A, B);
    dp[1][1] = 1;
    for (int i = 2; i <= N; ++i) {
        int nw = i & 1, pv = (i - 1) & 1;
        for (int j = 1; j <= min(i, (N + 1) >> 1); ++j) {
            dp[nw][j] = 0;
            if (i == A || i == B) {
                dp[nw][j] += dp[pv][j] + dp[pv][j - 1];
                continue;
            }
            dp[nw][j] += dp[pv][j - 1] * (j - (i > A) - (i > B)) + dp[pv][j + 1] * j;//不能放头，不能放尾
        }
    }
    i64 v = dp[N & 1][1].val(); ps(v);
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49