高精度+搜索+质数 BZOJ1225 [HNOI2001] 求正整数

 // 高精度+搜索+质数 BZOJ1225 [HNOI2001] 求正整数
 // 思路：
 // http://blog.csdn.net/huzecong/article/details/8478689
 // M=p1^(t1)*p2^(t2)*p3^(t3)....
 // N=(t1+1)*(t2+1)*(t3+1)*(t4+1)...
 // 所以t最大到16，就可以暴力搜索了

 #include <bits/stdc++.h>
 using namespace std;
 #define LL long long
 const double inf = 123456789012345.0;
 const LL MOD =100000000LL;
 const int N =1e5+;
 #define clc(a,b) memset(a,b,sizeof(a))
 const double eps = 1e-;
 void fre(){freopen("in.txt","r",stdin);}
 void freout() {freopen("out.txt","w",stdout);}
 inline int read() {int x=,f=;char ch=getchar();while(ch>''||ch<'') {if(ch=='-') f=-;ch=getchar();}while(ch>=''&&ch<='') {x=x*+ch-'';ch=getchar();}return x*f;}

 int n;
 const int M=;
 const int p[]= {, , , , , , , , , , , , , , , };
 double Log[];
 class bignum  {
     public:
         LL num[N];
         int tot;
         bignum() {}
         bignum(LL x) {
             clear();
             while (x) num[tot++] = x % MOD, x /= MOD;
         }
         void clear(){
             tot = ;
             for (int i = ; i < N; ++i) num[i] = 0LL;
         }
         void operator *= (const int &x){
             for (int i = ; i < tot; ++i) num[i] *= x;
             for (int i = ; i < tot; ++i)
                 if (num[i] >= MOD) {
                     num[i + ] += num[i] / MOD;
                     num[i] %= MOD;
                 }
             while (num[tot]) {
                 if (num[tot] >= MOD) {
                     num[tot + ] += num[tot] / MOD;
                     num[tot] %= MOD;
                 }
                 ++tot;
             }
         }
         void print()  {
             printf("%lld", num[tot - ]);
             for (int i = tot - ; i >= ; --i)
             printf("%08lld", num[i]);
         }
 }ans();  

 int t[],ct[];
 double mn;
 int cnt;

 void dfs(int d,int x,int m,double tem){
     if(tem>mn) return;
     if(x==){
         if(tem<mn){
             mn=tem,cnt=d-;
             for(int i=;i<d;i++) t[i]=ct[i];
         }
     }
     for(int i=;i*i<=x&&i<=m;i++){
         if(!(x%i)){
             if(i!=){
                 ct[d]=i;
                 dfs(d+,x/i,i,tem+(double)Log[d]*(i-));
             }
             if(x/i<=m&&x/i!=i){
                 ct[d]=x/i;
                 dfs(d+,i,x/i,tem+(double)Log[d]*(x/i-));
             }
         }
     }
 }

 int main(){
     scanf("%d",&n);
     for(int i=;i<=;i++) Log[i]=(double)log(p[i]);
     mn=inf;
     cnt=;
     dfs(,n,n,0.0);
     for(int i=;i<=cnt;i++){
         for(int j=t[i]-;j>;j--){
             ans*=p[i];
         }
     }
     ans.print();
     return ;
 }