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ID题目提交者结果用时内存语言文件大小提交时间测评时间
#646051#6137. Sub-cycle Graphqinglu09WA 101ms6764kbC++141.4kb2024-10-16 21:04:502024-10-16 21:04:51

Judging History

你现在查看的是最新测评结果

  • [2024-10-16 21:04:51]
  • 评测
  • 测评结果:WA
  • 用时:101ms
  • 内存:6764kb
  • [2024-10-16 21:04:50]
  • 提交

answer

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl '\n'
#define debug(x) cout<<#x<<": "<<x<<endl
const ll mod=1e9+7;
const ll N=1e5+10;

ll qpow(ll a,ll b)
{
	ll ans=1;
	a%=mod;
	while(b)
	{
		if(b&1) ans=ans*a%mod;
		a=a*a%mod;
		b>>=1;
	}
	return ans;
}

ll f[N],g[N],inv[N];
ll t[N];
void init_inverse1()//求1开始的连续逆元
{
	inv[1]=1;
	for(int i=2;i<N;i++)
		inv[i]=(ll)(mod-mod/i)*inv[mod%i]%mod;
}

void init_combinatorial()
{
	init_inverse1();//用init_inverse2()会稍微快一点
	f[0]=g[0]=1;
	for(int i=1;i<N;i++)
		f[i]=(ll)f[i-1]*i%mod;
	for(int i=1;i<N;i++)
		g[i]=(ll)g[i-1]*inv[i]%mod;
}

ll getC(int n,int m)//n大m小
{
	if(n<m) return 0;
	return ((ll)f[n]*g[m]%mod)*g[n-m]%mod;
}

void solve()
{
	ll n,m;
	cin>>n>>m;
	if(m>n)
	{
		cout<<0<<endl;
		return;
	}
	else if(n==m)
	{
		cout<<f[n-1]*qpow(2,mod-2)%mod<<endl;
		return;
	}
	ll k=n-m;
	ll ans=qpow(qpow(2,mod-2),k);
	ll now=0;
	for(int i=0;i<=n-k;i++)
	{
		now+=(t[k-i]*getC(k,i)%mod)*(getC(n-i-1,n-k-i)%mod)*qpow(-1,i%2);
		now%=mod;
	}
	ans=ans*now%mod;
	ans=ans*f[n]%mod;
	ans=ans*g[k]%mod;
	cout<<ans<<endl;
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	
	int T=1;
	cin>>T;
	init_combinatorial();
	t[0]=1;
	for(int i=1;i<N;i++) t[i]=t[i-1]*2%mod;
	while(T--)
	{
		solve();
	}

	return 0;
}

詳細信息

Test #1:

score: 100
Accepted
time: 3ms
memory: 6764kb

input:

3
4 2
4 3
5 3

output:

15
12
90

result:

ok 3 number(s): "15 12 90"

Test #2:

score: -100
Wrong Answer
time: 101ms
memory: 6724kb

input:

17446
3 0
3 1
3 2
3 3
4 0
4 1
4 2
4 3
4 4
5 0
5 1
5 2
5 3
5 4
5 5
6 0
6 1
6 2
6 3
6 4
6 5
6 6
7 0
7 1
7 2
7 3
7 4
7 5
7 6
7 7
8 0
8 1
8 2
8 3
8 4
8 5
8 6
8 7
8 8
9 0
9 1
9 2
9 3
9 4
9 5
9 6
9 7
9 8
9 9
10 0
10 1
10 2
10 3
10 4
10 5
10 6
10 7
10 8
10 9
10 10
11 0
11 1
11 2
11 3
11 4
11 5
11 6
11 7
11...

output:

1
3
3
1
1
6
15
12
3
1
10
45
90
60
12
1
15
105
375
630
360
60
1
21
210
1155
3465
5040
2520
360
1
28
378
2940
13545
35280
45360
20160
2520
1
36
630
6552
42525
170100
393120
453600
181440
20160
1
45
990
13230
114345
643545
2286900
4762800
4989600
1814400
181440
1
55
1485
24750
273735
2047815
10239075
3...

result:

wrong answer 275th numbers differ - expected: '157982055', found: '-842017952'