CodeChef October Challenge 2013 Editorial [Maxim and Dividers]

Problem: Maxim and Dividers
for a number N, by remove any digit from it, if it became a lucky* number, N is overlucky number.
you will be given a number, you have to calculate how many of its divisors is overlucky.

Observation: any number having at least one 4 or 7 is overlucky number.

first, make a function isOverlucky() to check weather a number overlucky or not.
now, loop for 1 to square root to find all its divisors and check them.

code:

1. #include<bits/stdc++.h>
2. using namespace std;
3.  
4. bool isOverlucky(int n)
5. {
6. while(n)
7. {
8. if(n%10==4 || n%10==7)
9. return true;
10. n/=10;
11. }
12. return false;
13. }
14.  
15. int main()
16. {
17. int tc,kk=1, n;
18. cin>>tc;
19. while(tc--)
20. {
21. cin>>n;
22. int sq=sqrt(n), ans=0;
23. for(int i=1;i<=sq;i++)
24. {
25. if(n%i==0)
26. {
27. if(overlucky(i))
28. ans++;
29. if(overlucky(n/i))
30. ans++;
31. }
32. }
33. if(sq*sq==n) if(isOverlucky(sq)) ans--;
34. cout<<ans<<endl;
35. }
36. return 0;
37. }

 Note: if N is square number, then it is calculating twice, don't forget to check that.

*lucky number: any number having the digit only 4 and 7 is lucky number.
example: 4, 444, 74744, 777 etc.