結果

問題 No.834 Random Walk Trip
ユーザー fiord
提出日時 2019-05-29 09:54:31
言語 C++14
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 221 ms / 2,000 ms
コード長 3,774 bytes
コンパイル時間 1,237 ms
コンパイル使用メモリ 125,360 KB
実行使用メモリ 23,416 KB
最終ジャッジ日時 2024-09-17 15:58:11
合計ジャッジ時間 3,082 ms
ジャッジサーバーID
（参考情報） 		judge4 / judge5
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ファイルパターン 結果
other AC * 26
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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

#define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <string>
#include <vector>
#include <utility>
#include <complex>
#include <set>
#include <map>
#include <unordered_map>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <limits>
#include <algorithm>
#include <array>
#include <random>
#include <complex>
#include <regex>
using namespace std;
typedef long double ld;
typedef long long ll;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef complex<ld> compd;
#define quickIO()   {cin.tie(0);    cout.sync_with_stdio(false);}
#define reach(i,a)  for(auto i:a)
#define rep(i,n)    for(int i=0;i<((int)n);i++)
#define REP(i,n)    for(int i=0;i<=((int)n);i++)
#define srep(i,a,n) for(int i=a;i<((int)n);i++)
#define SREP(i,a,n) for(int i=a;i<=((int)n);i++)
#define rrep(i,n)   for(int i=n-1;i>=0;i--)
#define RREP(i,n)   for(int i=n;i>=0;i--)
#define all(a)  (a).begin(),(a).end()
#define mp(a,b) make_pair(a,b)
#define mt  make_tuple
#define pb  push_back
template<typename T> istream & operator >> (istream & is, vector<T> & vec) {
    for (T& x : vec)    is >> x;
    return is;
}
template<typename T> ostream& operator << (ostream & os, vector<T> & vec) {
    os << "[";
    rep(i, vec.size())  os << (i ? ", " : "") << vec[i];
    os << "]";
    return os;
}
template<typename T> istream & operator >> (istream & is, pair<T, T> & p) {
    is >> p.first >> p.second;
    return is;
}
template<typename T> ostream& operator << (ostream & os, pair<T, T> & p) {
    os << p.first << " " << p.second;
    return os;
}
int bitcnt(ll x) {
    x = ((x & 0xAAAAAAAAAAAAAAAA) >> 1) + (x & 0x5555555555555555);
    x = ((x & 0xCCCCCCCCCCCCCCCC) >> 2) + (x & 0x3333333333333333);
    x = ((x & 0xF0F0F0F0F0F0F0F0) >> 4) + (x & 0x0F0F0F0F0F0F0F0F);
    x = ((x & 0xFF00FF00FF00FF00) >> 8) + (x & 0x00FF00FF00FF00FF);
    x = ((x & 0xFFFF0000FFFF0000) >> 16) + (x & 0x0000FFFF0000FFFF);
    x = ((x & 0xFFFFFFFF00000000) >> 32) + (x & 0x00000000FFFFFFFF);
    return x;
}
int bitcnt(int x) {
    x = ((x & 0xAAAAAAAA) >> 1) + (x & 0x55555555);
    x = ((x & 0xCCCCCCCC) >> 2) + (x & 0x33333333);
    x = ((x & 0xF0F0F0F0) >> 4) + (x & 0x0F0F0F0F);
    x = ((x & 0xFF00FF00) >> 8) + (x & 0x00FF00FF);
    x = ((x & 0xFFFF0000) >> 16) + (x & 0x0000FFFF);
    return x;
}
ll sqrtll(ll x) {
    ll left = 0, right = x;
    rep(i, 100) {
        ll mid = (left + right) >> 1;
        if (mid * mid <= x) left = mid;
        else    right = mid;
    }
    return left;
}
ll gcd(ll a, ll b) {
    return b == 0 ? a : gcd(b, a % b);
}
#define debug(x)    printf("Case #%d: ", x)
#define DEBUG 0
const ld infl = 1e100;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;
const ll inf = 1e18;
const int dx[] = { 1,0,-1,0,0 };
const int dy[] = { 0,1,0,-1,0 };
ll frac[2000010], inv_frac[2000010];
ll powmod(ll a, ll b) {
    ll ret = 1;
    while (b > 0) {
        if (b & 1)  ret = (ret * a) % mod;
        a = (a * a) % mod;
        b >>= 1;
    }
    return ret;
}
ll nCm(ll n, ll m) {
    return frac[n] * (inv_frac[m] * inv_frac[n - m] % mod) % mod;
}
int main() {
    ll n, m;    cin >> n >> m;
    if (n == 1) {
        cout << 1 << endl;
        return 0;
    }
    frac[0] = frac[1] = inv_frac[0] = inv_frac[1] = 1;
    SREP(i, 2, m) {
        frac[i] = frac[i - 1] * i % mod;
        inv_frac[i] = inv_frac[i - 1] * powmod(i, mod - 2) % mod;
    }
    ll pos = -m;
    ll ret = 0;
    while (pos <= m) {
        // (-2n, -2n+1), (0, 1), (2n, 2n+1), ...
        int pos_mod = ((pos % (2 * n)) + 2 * n) % (2 * n);
        if (pos_mod == 0 || pos_mod == 1) {
            // k = m - posとして、mCpos * kC(k/2)
            int abs_pos = abs(pos);
            int k = m - abs_pos;
            if (k % 2 == 0) {
                (ret += nCm(m, abs_pos + k / 2)) %= mod;
            }
        }
        pos++;
    }
    cout << ret << endl;
    return 0;
}
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