HDU5976 Detachment

Posted 2020-09-06 BBBob

 1 /*
 2  HDU5976 Detachment
 3  http://acm.hdu.edu.cn/showproblem.php?pid=5976
 4  数论 等差数列
 5  *
 6  *
 7  */
 8 #include <cstdio>
 9 #include <algorithm>
10 #include <vector>
11 using namespace std;
12 const int mod=1000000007;
13 const int Nmax=50001;
14 vector<long long> v;
15 long long f[Nmax];
16 long long g[Nmax];
17 long long qpow(long long base,int n)
18 {
19     long long ans=1LL;
20     base=base%mod;
21     while(n>0)
22     {
23         if(n&1)
24             ans=ans*base%mod;
25         base=(base*base)%mod;
26         n>>=1;
27     }
28     while(ans<0)
29         ans+=mod;
30     return ans;
31 }
32 
33 int main()
34 {
35     //freopen("3.in","r",stdin);
36     int t;
37     scanf("%d",&t);
38     long long x;
39     f[1]=1LL;
40      
41     f[0]=0LL;
42     f[2]=2LL;
43     g[1]=1LL;
44     g[2]=2LL;
45     v.push_back(f[1]);
46     v.push_back(f[2]);
47     for(int i=3;i<Nmax;i++)
48     {
49         g[i]=1LL*i*g[i-1]%mod;
50         f[i]=1LL*i+f[i-1];
51         v.push_back(f[i]);
52     }
53     //printf("%lld\n",f[Nmax-1]);
54     while(t--)
55     {
56         long long ans=1LL;
57         scanf("%lld",&x);
58         int j=1;
59         int k=1;
60         for(int i=1;i<Nmax;i++)
61         {
62             if(x>=f[i] && x<f[i+1])
63             {
64                 j=i;
65                 break;
66             }
67         }
68         //printf("bj:%d\n",j);
69         j=lower_bound(v.begin(),v.end(),x)-v.begin();
70         while(!(x>=f[j]&& x<f[j+1]))
71             j++;
72         //printf("j:%d\n",j);
73         long long remain=x-f[j];
74         if(remain)
75         {
76             if(remain==j)
77                 k=2;
78             else
79                 k=j+1-remain;
80             //printf("j:%d k:%d\n",j,k);
81             ans=g[j];
82             ans=ans*qpow(1LL*k, mod-2 )%mod;
83             ans=ans*(k+remain)%mod;
84         }
85         else 
86         {
87             ans=g[j];
88         }
89         while(ans<0)
90             ans+=mod;
91         printf("%lld\n",ans);
92     }
93     return 0;
94 }