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IDProblemSubmitterResultTimeMemoryLanguageFile sizeSubmit timeJudge time
#808964#6137. Sub-cycle GraphlichenghanAC ✓85ms6184kbC++171.1kb2024-12-11 10:02:162024-12-11 10:02:17

Judging History

你现在查看的是最新测评结果

  • [2024-12-11 10:02:17]
  • 评测
  • 测评结果:AC
  • 用时:85ms
  • 内存:6184kb
  • [2024-12-11 10:02:16]
  • 提交

answer

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int L=2e5+10;
const int mod=1e9+7;
inline constexpr int qpow(ll x,ll y=mod-2){
	ll r=1;
	for(x%=mod;y;y>>=1,x=x*x%mod) if(y&1) r=r*x%mod;
	return r;
}
int fac[L],ifac[L];
int p[L];
void init_fac(){
	fac[0]=ifac[0]=1;
	for(int i=1;i<L;i++) fac[i]=(ll)fac[i-1]*i%mod;
	ifac[L-1]=qpow(fac[L-1]);
	for(int i=L-2;i>=1;i--) ifac[i]=(ll)ifac[i+1]*(i+1)%mod;
	p[0]=1; p[1]=mod-qpow(2);
	for(int i=2;i<L;i++) p[i]=(ll)p[i-1]*p[1]%mod;
}
int binom(int u,int d){
	if(d<0||d>u) return 0;
	return (ll)fac[u]*ifac[d]%mod*ifac[u-d]%mod;
}
void solve(){
	int n,m;
	scanf("%d%d",&n,&m);
	if(m>n) puts("0");
	else if(m==n) printf("%lld\n",(ll)fac[n-1]*qpow(2)%mod);
	else {
		int ans=0;
		int c=n-m;
		for(int i=0;i<=c;i++) {
			ans=(ans+(ll)p[i]*binom(c,i)%mod*binom(c-1+n-c-i,c-1))%mod;
			// printf("%d: %d\n",i,(ll)qpow(mod-qpow(2),i)*binom(c,i)%mod*binom(c-1+n-c-i,c-1)%mod);
		}
		ans=(ll)ans*fac[n]%mod*ifac[c]%mod;
		printf("%d\n",ans);
	}
}
signed main(){
	init_fac();
	signed tc;
	scanf("%d",&tc);
	while(tc--){
		solve();
	}
}

Details

Tip: Click on the bar to expand more detailed information

Test #1:

score: 100
Accepted
time: 0ms
memory: 6108kb

input:

3
4 2
4 3
5 3

output:

15
12
90

result:

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

Test #2:

score: 0
Accepted
time: 85ms
memory: 6184kb

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:

ok 17446 numbers