Problem Link : http://lightoj.com:81/volume/problem/1276

Solution Idea:

Just pre-calculate the numbers and then run binary search.

#include <bits/stdc++.h>

#define pii              pair <int,int>
#define pll              pair <long long,long long>
#define sc               scanf
#define pf               printf
#define Pi               2*acos(0.0)
#define ms(a,b)          memset(a, b, sizeof(a))
#define pb(a)            push_back(a)
#define MP               make_pair
#define db               double
#define ll               long long
#define EPS              10E-10
#define ff               first
#define ss               second
#define sqr(x)           (x)*(x)
#define D(x)             cout<<#x " = "<<(x)<<endl
#define VI               vector <int>
#define DBG              pf("Hi\n")
#define MOD              1000000007
#define CIN              ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define SZ(a)            (int)a.size()
#define sf(a)            scanf("%d",&a)
#define sfl(a)           scanf("%lld",&a)
#define sff(a,b)         scanf("%d %d",&a,&b)
#define sffl(a,b)        scanf("%lld %lld",&a,&b)
#define sfff(a,b,c)      scanf("%d %d %d",&a,&b,&c)
#define sfffl(a,b,c)     scanf("%lld %lld %lld",&a,&b,&c)
#define stlloop(v)       for(__typeof(v.begin()) it=v.begin();it!=v.end();it++)
#define loop(i,n)        for(int i=0;i<n;i++)
#define loop1(i,n)       for(int i=1;i<=n;i++)
#define REP(i,a,b)       for(int i=a;i<b;i++)
#define RREP(i,a,b)      for(int i=a;i>=b;i--)
#define TEST_CASE(t)     for(int z=1;z<=t;z++)
#define PRINT_CASE       printf("Case %d: ",z)
#define CASE_PRINT       cout<<"Case "<<z<<": "
#define all(a)           a.begin(),a.end()
#define intlim           2147483648
#define infinity         (1<<28)
#define ull              unsigned long long
#define gcd(a, b)        __gcd(a, b)
#define lcm(a, b)        ((a)*((b)/gcd(a,b)))

using namespace std;


/*----------------------Graph Moves----------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

/*-----------------------Bitmask------------------*/
//int Set(int N,int pos){return N=N | (1<<pos);}
//int reset(int N,int pos){return N= N & ~(1<<pos);}
//bool check(int N,int pos){return (bool)(N & (1<<pos));}
/*------------------------------------------------*/

vector<ll>v;
int cnt=0;
void func(ll n)
{
    if(n>1000000000000ULL) return;
    if(n!=0)
        v.pb(n);
    func(n*10+4);
    func(n*10+7);
}

int id;
ll maxx=1000000000000;

vector<ll>lucky;

void gen_num(int idx,ll num)
{
    if(idx>=SZ(v)) return ;
    for(int i=idx; i<SZ(v); i++)
    {
        ll temp=num*v[i];
        if(temp<=0 || temp>=maxx) return;
        lucky.pb(temp);
        gen_num(i,temp);
    }
}

int main()
{

//    freopen("in.txt","r",stdin);
    ///freopen("out.txt","w",stdout);

    func(0);
    sort(all(v));

    gen_num(0,1);
    
    set<ll> st(all(lucky));
    lucky.assign(all(st));
    
    int t;
    sf(t);
    
    TEST_CASE(t)
    {
        ll a,b;
        sffl(a,b);
        ll r=upper_bound(all(lucky),b)-lucky.begin();
        ll l=lower_bound(all(lucky),a)-lucky.begin();
        int ans=(r-l);
        PRINT_CASE;
        pf("%d\n",ans);
    }

    return 0;
}