Codeforces 414B Mashmokh and ACM

http://codeforces.com/problemset/problem/414/B

题目大意：

题意:一个序列B1,B2...Bl如果是好的,必须满足Bi | Bi + 1(a | b 代表a整除b), 求长度为K,元素大小小于等于N的序列个数

思路:f[i][j] 代表在序列的第i位，当前数字为j的方案数

 1 #include<cstdio>
 2 #include<cmath>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<iostream>
 6 const int Mod=1000000007;
 7 int f[5005][5005];
 8 int n,K;
 9 int read(){
10     int t=0,f=1;char ch=getchar();
11     while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
12     while ('0'<=ch&&ch<='9'){t=t*10+ch-'0';ch=getchar();}
13     return t*f;
14 }
15 int main(){
16     n=read();K=read();
17     for (int i=1;i<=n;i++)
18      f[1][i]=1;
19     for (int i=2;i<=K;i++)
20      for (int j=1;j<=n;j++){
21         for (int k=1;k<=sqrt(j);k++)
22          if (j%k==0){
23                 f[i][j]=(f[i][j]+f[i-1][k])%Mod;
24                 if (k*k!=j)
25                 f[i][j]=(f[i][j]+f[i-1][j/k])%Mod;
26          }
27      }
28     int ans=0;
29     for (int i=1;i<=n;i++)
30      ans=(ans+f[K][i])%Mod;
31     printf("%d
",ans);  
32     return 0;
33 }