BZOJ2111: [ZJOI2010]Perm 排列计数

 1 #include<cstdio>
 2 
 3 #include<cstdlib>
 4 
 5 #include<cmath>
 6 
 7 #include<cstring>
 8 
 9 #include<algorithm>
10 
11 #include<iostream>
12 
13 #include<vector>
14 
15 #include<map>
16 
17 #include<set>
18 
19 #include<queue>
20 
21 #include<string>
22 
23 #define inf 1000000000
24 
25 #define maxn 2000000+5
26 
27 #define maxm 200000+5
28 
29 #define eps 1e-10
30 
31 #define ll long long
32 
33 #define pa pair<int,int>
34 
35 #define for0(i,n) for(int i=0;i<=(n);i++)
36 
37 #define for1(i,n) for(int i=1;i<=(n);i++)
38 
39 #define for2(i,x,y) for(int i=(x);i<=(y);i++)
40 
41 #define for3(i,x,y) for(int i=(x);i>=(y);i--)
42 
43 #define for4(i,x) for(int i=head[x],y=e[i].go;i;i=e[i].next,y=e[i].go)
44 
45 #define for5(n,m) for(int i=1;i<=n;i++)for(int j=1;j<=m;j++)
46 
47 #define mod 1000000007
48 
49 using namespace std;
50 
51 inline int read()
52 
53 {
54 
55     int x=0,f=1;char ch=getchar();
56 
57     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
58 
59     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}
60 
61     return x*f;
62 
63 }
64 int s[maxn];
65 ll  n,m,p,f[maxn],fac[maxn],inv[maxn];
66 inline ll c(int n,int m)
67 {
68     if(n<m)return 0;
69     if(n<p&&m<p)return fac[n]*inv[m]%p*inv[n-m]%p;
70     return c(n/p,m/p)*c(n%p,m%p)%p;
71 }
72 
73 int main()
74 
75 {
76 
77     freopen("input.txt","r",stdin);
78 
79     freopen("output.txt","w",stdout);
80 
81     n=read();p=read();m=min(n,p-1);
82     fac[0]=1;
83     for1(i,m)fac[i]=fac[i-1]*(ll)i%p;
84     inv[0]=inv[1]=1;
85     for2(i,2,m)inv[i]=(ll)(p/i+1)*inv[i-p%i]%p;
86     for2(i,2,m)inv[i]=inv[i]*inv[i-1]%p;
87     for3(i,n,1)
88     {
89         s[i]=s[i<<1]+s[i<<1|1]+1;
90         f[i]=((i<<1)>n?1:f[i<<1])*((i<<1|1)>n?1:f[i<<1|1])%p*c(s[i]-1,s[i<<1])%p;
91     }
92     cout<<f[1]<<endl;
93 
94     return 0;
95 
96 }