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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
#818924#6137. Sub-cycle Graphfairyqq28AC ✓355ms472608kbC++141.1kb2024-12-18 10:53:352024-12-18 10:53:36

Judging History

你现在查看的是最新测评结果

  • [2024-12-18 10:53:36]
  • 评测
  • 测评结果:AC
  • 用时:355ms
  • 内存:472608kb
  • [2024-12-18 10:53:35]
  • 提交

answer

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#define rep(i, a, b) for(int i = (a); i <= (b); i++)
#define per(i, a, b) for(int i = (a); i >= (b); i--)
using namespace std;
typedef long long ll;
const int N = 30000010;
const ll mod = 1000000007, inv2 = (mod+1)>>1;
ll qpow(ll x, ll y = mod - 2){
	ll ret = 1;
	for(; y; y >>= 1, (x *= x) %= mod) if(y & 1) (ret *= x) %= mod;
	return ret;
}
ll fac[N], ifac[N];

ll C(ll x, ll y){
	if(x < y || y < 0) return 0;
	return fac[x] * ifac[x-y] % mod * ifac[y] % mod;
}

int n;
ll m, ans;
void solve(){
	scanf("%d%lld", &n, &m);
	if(!m) {puts("1"); return;}
	if(n < m) {puts("0"); return;}
	if(n == m) {printf("%lld\n", fac[n-1] * inv2 % mod); return;}
	ll pw = 1;
	ans = 0;
	rep(i, 1, n-m){
		(pw *= inv2) %= mod;
		(ans += C(n-m, i) * C(m-1, i-1) % mod * pw) %= mod;
	}
	(ans *= fac[n] * ifac[n-m] % mod) %= mod;
	printf("%lld\n", ans);
}

int main(){
	fac[0] = 1; rep(i, 1, N-5) fac[i] = fac[i-1] * i % mod;
	ifac[N-5] = qpow(fac[N-5]);
	per(i, N-6, 0) ifac[i] = ifac[i+1] * (i+1) % mod;
	int T; scanf("%d", &T); while(T--) solve();
	return 0;
}

詳細信息

Test #1:

score: 100
Accepted
time: 283ms
memory: 472604kb

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: 355ms
memory: 472608kb

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