BZOJ1853: [Scoi2010]幸运数字

#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstdio>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define maxn 20050
#define ll long long
using namespace std;
ll l,r,ans,a[maxn],b[maxn];
int n,m,vis[maxn];
ll read(){
    ll x=0,f=1; char ch=getchar();
    while (!isdigit(ch)) {
        if (ch==‘-‘) f=-1; ch=getchar();
    }
    while (isdigit(ch)){
        x=x*10+ch-‘0‘; ch=getchar();
    }
    return x*f;
}
void pre(ll x){
    if (x>r) return;
    if (x!=0&&x<=r) a[++m]=x;
    pre(x*10+6);
    pre(x*10+8);
}
ll gcd(ll x,ll y){
    if (y==0) return x;
    return gcd(y,x%y);
}
void dfs(int x,int y,ll z){
    if (x>n){
        if (y&1) ans+=r/z-(l-1)/z;
        else if (y)ans-=r/z-(l-1)/z;
        return ;
    }
    dfs(x+1,y,z);
    ll tmp=z/gcd(z,a[x]);
    if (((double)a[x]*tmp)<=r) dfs(x+1,y+1,a[x]*tmp);
}
int main(){
    l=read(); r=read();
    pre(0);
    sort(a+1,a+m+1);
    rep(i,1,m) if (!vis[i]){
        b[++n]=a[i];
        rep(j,i+1,m){
            if (a[j]%a[i]==0&&vis[j]==0) vis[j]=1;
        }
    }
    rep(i,1,n) a[n-i+1]=b[i];
    dfs(1,0,1);
    printf("%lld\n",ans);
    return 0;
}