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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
#94183#6137. Sub-cycle Graphinstallb#AC ✓87ms4680kbC++141.1kb2023-04-05 14:48:522023-04-05 14:48:54

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.
  • [2023-04-05 14:48:54]
  • 评测
  • 测评结果:AC
  • 用时:87ms
  • 内存:4680kb
  • [2023-04-05 14:48:52]
  • 提交

answer

#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=(l);i<=(r);++i)
#define per(i,r,l) for(int i=(r);i>=(l);--i)
using namespace std;
const int N=1e5+10,P=1e9+7;
int fac[N],ifac[N],f[N],n,m,T;
inline int ksm(int a,int b){
    int ans=1;
    for(;b;b>>=1,a=1ll*a*a%P) if(b&1) ans=1ll*ans*a%P;
    return ans;
}
inline int C(int n,int k){
    if(n<k||k<0) return 0;
    return 1ll*fac[n]*ifac[k]%P*ifac[n-k]%P;
}
void pre(int n){
    f[0]=fac[0]=ifac[0]=1;int tt=(P+1)>>1;
    rep(i,1,n) fac[i]=1ll*fac[i-1]*i%P;ifac[n]=ksm(fac[n],P-2);
    per(i,n,1) ifac[i-1]=1ll*ifac[i]*i%P;
    rep(i,1,n) f[i]=1ll*tt*f[i-1]%P;
}
int main(){
    pre(1e5);scanf("%d",&T);
    while(T--){
        scanf("%d%d",&n,&m);
        if(n<m){puts("0");continue;}
        if(n==m){printf("%lld\n",1ll*fac[n-1]*ifac[2]%P);continue;}
        if(m==0){puts("1");continue;}
        int w=n-m,ans=0;
        rep(i,0,w){
            int p=1ll*f[w-i]%P*C(w,i)%P;
            int q=C(m-1,w-i-1);
            ans=(ans+1ll*p*q)%P;
        }
        printf("%lld\n",1ll*ans*ifac[w]%P*fac[n]%P);
    }
    return 0;
}

详细

Test #1:

score: 100
Accepted
time: 4ms
memory: 4660kb

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: 87ms
memory: 4680kb

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