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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
#93971#6137. Sub-cycle GraphksunhokimAC ✓129ms5140kbC++201.3kb2023-04-04 12:03:532023-04-04 12:03:55

Judging History

你现在查看的是最新测评结果

  • [2023-08-10 23:21:45]
  • System Update: QOJ starts to keep a history of the judgings of all the submissions.
  • [2023-04-04 12:03:55]
  • 评测
  • 测评结果:AC
  • 用时:129ms
  • 内存:5140kb
  • [2023-04-04 12:03:53]
  • 提交

answer

#include <bits/stdc++.h>
#define MAXN ((int) 1e5)
#define MOD ((int) 1e9 + 7)
using namespace std;

int n;
long long ans, m;

long long fac[MAXN + 10], ifac[MAXN + 10];

long long C(int a, int b) {
    return fac[a] * ifac[b] % MOD * ifac[a - b] % MOD;
}

void solve() {
    scanf("%d%lld", &n, &m);
    if (m == 0) printf("1\n");
    else if (m > n) printf("0\n");
    else if (m == n) printf("%lld\n", fac[n - 1] * ifac[2] % MOD);
    else {
        ans = 0;
        // f is the \prod in the tutorial
        long long f = 1;
        for (int i = 1; i <= n - m; i++) {
            if (m + i < i * 2) continue;
            long long t = C(m + i, i * 2) * f % MOD;
            f = f * (i * 2 + 1) % MOD;
            t = t * fac[m - i] % MOD;
            t = t * C(m - 1, i - 1) % MOD;
            ans = (ans + C(n, n - m - i) * t) % MOD;
        }
        printf("%lld\n", ans);
    }
}

int main() {
    fac[0] = 1;
    for (int i = 1; i <= MAXN; i++) fac[i] = fac[i - 1] * i % MOD;
    ifac[0] = ifac[1] = 1;
    for (int i = 2; i <= MAXN; i++) ifac[i] = (MOD - MOD / i) * ifac[MOD % i] % MOD;
    for (int i = 2; i <= MAXN; i++) ifac[i] = ifac[i - 1] * ifac[i] % MOD;

    int tcase; scanf("%d", &tcase);
    while (tcase--) solve();
    return 0;
}

詳細信息

Test #1:

score: 100
Accepted
time: 2ms
memory: 5140kb

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: 129ms
memory: 5116kb

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