結果

問題 No.391 CODING WAR
ユーザー anta
提出日時 2016-07-08 22:38:31
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 21 ms / 2,000 ms
コード長 2,916 bytes
コンパイル時間 1,494 ms
コンパイル使用メモリ 170,020 KB
実行使用メモリ 5,248 KB
最終ジャッジ日時 2024-10-13 04:37:22
合計ジャッジ時間 2,326 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge2
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 4
other AC * 16
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ソースコード

diff #
プレゼンテーションモードにする

#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> static void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> static void amax(T &x, U y) { if(x < y) x = y; }
template<int MOD>
struct ModInt {
    static const int Mod = MOD;
    unsigned x;
    ModInt() : x(0) {}
    ModInt(signed sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
    ModInt(signed long long sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
    int get() const { return (int)x; }
    ModInt &operator+=(ModInt that) { if((x += that.x) >= MOD) x -= MOD; return *this; }
    ModInt &operator-=(ModInt that) { if((x += MOD - that.x) >= MOD) x -= MOD; return *this; }
    ModInt &operator*=(ModInt that) { x = (unsigned long long)x * that.x % MOD; return *this; }
    ModInt &operator/=(ModInt that) { return *this *= that.inverse(); }
    ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
    ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
    ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
    ModInt operator/(ModInt that) const { return ModInt(*this) /= that; }
    ModInt inverse() const {
        signed a = x, b = MOD, u = 1, v = 0;
        while(b) {
            signed t = a / b;
            a -= t * b; std::swap(a, b);
            u -= t * v; std::swap(u, v);
        }
        if(u < 0) u += Mod;
        ModInt res; res.x = (unsigned)u;
        return res;
    }
    bool operator==(ModInt that) const { return x == that.x; }
    bool operator!=(ModInt that) const { return x != that.x; }
    ModInt operator-() const { ModInt t; t.x = x == 0 ? 0 : Mod - x; return t; }
};
template<int MOD> ModInt<MOD> operator^(ModInt<MOD> a, unsigned long long k) {
    ModInt<MOD> r = 1;
    while(k) {
        if(k & 1) r *= a;
        a *= a;
        k >>= 1;
    }
    return r;
}
typedef ModInt<1000000007> mint;
vector<mint> fact, factinv;
void nCr_computeFactinv(int N) {
    N = min(N, mint::Mod - 1);
    fact.resize(N + 1); factinv.resize(N + 1);
    fact[0] = 1;
    rer(i, 1, N) fact[i] = fact[i - 1] * i;
    factinv[N] = fact[N].inverse();
    for(int i = N; i >= 1; i --) factinv[i - 1] = factinv[i] * i;
}
mint nCr(int n, int r) {
    if(n >= mint::Mod)
        return nCr(n % mint::Mod, r % mint::Mod) * nCr(n / mint::Mod, r / mint::Mod);
    return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}
int main() {
    long long N; int M;
    while(~scanf("%lld%d", &N, &M)) {
        nCr_computeFactinv(M);
        mint ans;
        rer(i, 0, M) {
            mint cnt = nCr(M, i);
            cnt *= mint(M - i) ^ N;
            if(i % 2 == 0)
                ans += cnt;
            else
                ans -= cnt;
        }
        printf("%d\n", ans.get());
    }
    return 0;
}
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