E:幸运数字Ⅱ
幸运数字Ⅱ
https://ac.nowcoder.com/acm/problem/15291
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e5+5;
ll a[N],cnt=2;
void dfs(ll x){
if(x>1e9) return;
if(x>10) a[cnt++]=x;
dfs(x*10+4);
dfs(x*10+7);
}
int main(){
ll l,r;
a[0]=4,a[1]=7;
dfs(4);
dfs(7);
a[cnt]=4444444444;
sort(a,a+cnt+1);
cin>>l>>r;
int p1=lower_bound(a,a+cnt+1,l)-a,p2=lower_bound(a,a+cnt+1,r)-a;
ll ans=0;
for(int i=p1;i<=p2;i++){
ans+=(min(a[i],r)-l+1)*a[i];
l=a[i]+1;
}
cout<<ans<<endl;
return 0;
}