QOJ.ac
QOJ
ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#164055 | #6736. Alice and Bob | yujie3 | TL | 0ms | 0kb | C++14 | 4.1kb | 2023-09-04 19:12:06 | 2023-09-04 19:12:06 |
answer
#include<bits/stdc++.h>
#define endl '\n'
#define fast() ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr)
#define F first
#define S second
#define lowbit(x) ((x) & (-x))
#define _ int _T; cin >> _T; while(_T --)
//#define int long long
#define no cout << "NO" << endl
#define yes cout << "YES" << endl
using namespace std;
typedef pair<int, int> PII;
typedef pair<char,int> PCI;
typedef long long ll;
const int N = 1e7 + 5;
const int MOD = 1e9 + 7;
const ll mod = 998244353;
int n,m,k;
//int a[N];
//int tree[N];
//int b[N],c[N];
//PII p[N];
//PCI pc[N];
string s;
ll fac[N]; //阶乘
ll inv[N]; //逆元
ll quickMod(ll a,ll b)
{
ll ans = 1;
while (b)
{
if (b&1)
ans = ans * a % mod;
a = a*a % mod;
b >>= 1;
}
return ans;
}
void getFac()
{
fac[0] = inv[0] = 1;
for (int i = 1 ; i <= N ; i++)
{
fac[i] = fac[i-1] * i % mod;
inv[i] = quickMod(fac[i],mod-2); //表示i的阶乘的逆元
}
}
ll getC(ll n,ll m) //C(n,m) = n!/((n-m)!*m!) % (1e9+7)
{
return fac[n] * inv[n-m] % mod;
}
//int fact[N];
//int inv[N];
//
//int qpow(int a,int b,int p)
//{
// int res = 1;
// while (b)
// {
// if (b & 1)
// res = (res * a) % p;
// a = (a * a) % p;
// b /= 2;
// }
// return res % p;
//}
//
//void init()
//{
// fact[0] = 1;
// for (int i = 1; i <= N; i++)
// fact[i] = (fact[i - 1] * i) % mod;
// inv[N] = qpow(fact[N], mod - 2, mod);
// for (int i = N - 1; i >= 0; i--)
// inv[i] = (inv[i + 1] * (i + 1)) % mod;
//}
//
//int _get(int u,int d)
//{
// if(u == 0) return 1;
// int ans = d; u --;
// for(int i = d - 1;u > 0;u --,i --)
// ans *= i,ans %= mod;
// return ans;
//}
void solve()
{
// cin >> n;
// for(int i = 1;i <= n;i ++)
// a[i] = i;
// do
// {
// for(int i = 1;i <= n;i ++)
// cout << a[i] << " ";
// cout << endl;
// }while(next_permutation(a + 1,a + 1 + n));
// cout << "------------------------------------" << endl;
cin >> n;
ll ans = 0;
for(int i = 1;i <= n;i ++)
{
if(n - i < i - 1) continue;
ans += getC(n - i,i - 1) * getC(n - i,n - i) % mod;
// ans += fact[n - i] * inv[n - i - (i - 1)] * fact[n - i] % mod;
// ans += _get(i - 1,n - i) * _get(n - i,n - i) % mod;
// cout << ans << " " << i << " " << _get(i - 1,n - i) << " " << _get(n - i,n - i) << "****************" << endl;
// cout << fact[n - i] / fact[n - i - (i - 1)] << " " << fact[n - i] << "--------------- " << fact[n - i - (i - 1)] << " " << fact[n - i] << endl;
}
cout << ans % mod << endl;
}
signed main()
{
fast();
// _
// init();
getFac();
solve();
return 0;
}
/**
* ┏┓ ┏┓+ +
* ┏┛┻━━━┛┻┓ + +
* ┃ A C ┃
* ┃ ━ ┃ ++ + + +
* ████━████+
* ◥██◤ ◥██◤ +
* ┃ ┻ ┃
* ┃ ┃ + +
* ┗━┓ ┏━┛
* ┃ ┃ + + + +Code is far away from
* ┃ ┃ + bug with the animal protecting
* ┃ ┗━━━┓ 神兽保佑,代码无bug
* ┃ ┣┓
* ┃ ┏┛
* ┗┓┓┏━┳┓┏┛ + + + +
* ┃┫┫ ┃┫┫
* ┗┻┛ ┗┻┛+ + + +
*/
/*
_ooOoo_
o8888888o
88" . "88
(| -_- |)
O\ = /O
____/`---'\____
.' \\| |// `.
/ \\||| : |||// \
/ _||||| -:- |||||- \
| | \\\ - /// | |
| \_| ''\---/'' | |
\ .-\__ `-` ___/-. /
___`. .' /--.--\ `. . __
."" '< `.___\_<|>_/___.' >'"".
| | : `- \`.;`\ _ /`;.`/ - ` : | |
\ \ `-. \_ __\ /__ _/ .-` / /
======`-.____`-.___\_____/___.-`____.-'======
`=---='
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
A佛祖保佑C
*/
Details
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Test #1:
score: 0
Time Limit Exceeded
input:
1