【搜索】【约数个数定理】[HAOI2007]反素数ant

 1 #include<cstdio>
 2 #include<iostream>
 3 using namespace std;
 4 const int prime[]={0,2,3,5,7,11,13,17,19,23,29};
 5 int n,Time[11],sum;
 6 long long ans;
 7 int Calc()
 8 {
 9     int res=1;
10     for(int i=1;i<=10;i++)
11       res*=(Time[i]+1);
12     return res;
13 }
14 void dfs(long long now,int last)
15 {
16     if(now>n)
17       return;
18     int tmp=Calc();
19     if(sum<tmp||(sum==tmp&&now<ans)){sum=tmp;ans=now;}
20     for(int i=1;i<=10;i++)
21       if(Time[i]<Time[i-1]&&i>=last)
22         {
23             Time[i]++;
24             dfs(now*prime[i],i);
25             Time[i]--;
26         }
27 }
28 int main()
29 {
30     scanf("%d",&n);
31     Time[0]=2147483647;
32     dfs(1,0);
33     cout<<ans<<endl;
34     return 0;
35 }