bzoj1053: [HAOI2007]反素数ant

题面在这里
做法：
这题嘛看起来很恐怖啊= =n居然有20亿
然而其实我们只需枚举一下质因子的个数，而这个枚举量是很小的，因为前10个质数相乘就已经超过20亿了吧、、、
于是我取了前12个质数。
暴力dfs一下就行。

/*************************************************************    Problem: bzoj 1053 [HAOI2007]反素数ant    User: fengyuan    Language: C++    Result: Accepted    Time: 68 ms    Memory: 1296 kb    Submit_Time: 2017-12-15 00:36:32*************************************************************/#include<bits/stdc++.h>#define rep(i, x, y) for (int i = (x); i <= (y); i ++)#define down(i, x, y) for (int i = (x); i >= (y); i --)#define mid ((l+r)/2)#define lc (o<<1)#define rc (o<<1|1)#define pb push_back#define mp make_pair#define PII pair<int, int>#define F first#define S second#define B begin()#define E end()using namespace std;typedef long long LL;//headconst int p[13] = {0, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37};int n, ans, maxd;inline void dfs(LL now, int d, int k){    if (d > maxd || d == maxd && now < ans) ans = now, maxd = d;    if (k == 13) return;    LL a = 1; int i = 0;    while (1){        if (a*now > n) break;        dfs(a*now, d*(i+1), k+1);        a *= p[k];        i ++;    }}int main(){    scanf("%d", &n);    dfs(1, 1, 1);    printf("%d\n", ans);    return 0;}