[HNOI2001][luogu1128][bzoj1225] 求正整数

题目大意:求最小的x,使x的不同约数个数为给定值
设x=π(p[i]^mi[i])
其约数个数n=π(mi[i]+1)
于是爆搜n的组成方式即可
搜索过程中当前数能组成的最小数超过答案时退出搜索
ps:用指数存储比高精度高到不知哪里去了
Orz w_yqts

#include <bits/stdc++.h>using namespace std;#define eps (1e-9)int pr[17]={0,2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53};double lg[17],minx=(1e100);int f[233],a[233];int ans[100005],len,mi[17],mi1[17];int K;void cheng(const int x){    for (int i=1;i<=len;++i) ans[i]=ans[i]*x;    for (int i=1;i<=len;++i) ans[i+1]+=ans[i]/10,ans[i]%=10;    while (ans[len+1]) ++len,ans[len+1]+=ans[len]/10,ans[len]%=10;}void dfs(int k,int x,double f){    if (f+eps>minx) return;    if (x==1) {minx=f;for (int i=1;i<17;++i) mi[i]=mi1[i];return;}    if (k>16) return;    for (int i=2;i<=x;++i)    if (x%i==0)    {        mi1[k]=i-1;        dfs(k+1,x/i,f+lg[k]*(i-1));        mi1[k]=0;    }}int main(){    //for (int i=1;i<=36;++i){int t=0;for (int j=1;j<=i;++j) if (i%j==0) ++t;cout<<i<<' '<<t<<endl;}    for (int i=1;i<17;++i) lg[i]=log(pr[i]);    cin>>K;    dfs(1,K,0.0);    ans[1]=len=1;    for (int i=1;i<17;++i)    for (int j=1;j<=mi[i];++j) cheng(pr[i]);    for (int i=len;i;--i) printf("%d",ans[i]);}