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IDProblemSubmitterResultTimeMemoryLanguageFile sizeSubmit timeJudge time
#691507#6137. Sub-cycle GraphOIer_kzc#AC ✓132ms2384kbC++171.3kb2024-10-31 11:44:252024-10-31 11:44:25

Judging History

你现在查看的是最新测评结果

  • [2024-10-31 11:44:25]
  • 评测
  • 测评结果:AC
  • 用时:132ms
  • 内存:2384kb
  • [2024-10-31 11:44:25]
  • 提交

answer

#include <stdio.h>
#include <string.h>

#include <vector>
#include <algorithm>

#define eb emplace_back

#define LOG(FMT...) fprintf(stderr, FMT)

using namespace std;

typedef long long LL;

constexpr int N = 100005, mod = 1e9 + 7, inv2 = (mod + 1) / 2;

constexpr int inv(int x, int k = mod - 2) {
	int r = 1;
	while (k) {
		if (k & 1) {
			r = x * (LL)r % mod;
		}
		x = x * (LL)x % mod;
		k >>= 1;
	}
	return r;
}

int fact[N], infact[N];

void pref() {
	constexpr int n = N - 1;
	*fact = 1;
	for (int i = 1; i <= n; ++i) {
		fact[i] = fact[i - 1] * (LL)i % mod;
	}
	infact[n] = inv(fact[n]);
	for (int i = n; i; --i) {
		infact[i - 1] = infact[i] * (LL)i % mod;
	}
}

int C(int x, int y) {
	return y < 0 || x < y ? 0 : fact[x] * (LL)infact[y] % mod * infact[x - y] % mod;
}

int solve() {
	int n; LL m;
	scanf("%d%lld", &n, &m);
	if (m > n) return 0;
	if (m == n) return fact[n - 1] * (LL)inv2 % mod;
	m = n - m;
	constexpr int w = mod - inv2;
	int r = 1, s = 0;
	for (int k = 0; k <= m; ++k) {
		s = (s + C(n - k - 1, m - 1) * (LL)C(m, k) % mod * r) % mod;
		r = r * (LL)w % mod;
	}
	s = s * (LL)fact[n] % mod * infact[m] % mod;
	return s;
}

int main() {
	pref();
	int task;
	for (scanf("%d", &task); task--; ) {
		printf("%d\n", solve());
	}
	return 0;
}

Details

Tip: Click on the bar to expand more detailed information

Test #1:

score: 100
Accepted
time: 1ms
memory: 2360kb

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: 132ms
memory: 2384kb

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