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  1. #include<stdio.h>
  2. #include<string>
  3. #include<vector>
  4. #include<iostream>
  5. typedef long long int lli;
  6.  
  7. using namespace std;
  8. const long long int K = 1000000007LL;
  9.  
  10. lli power(lli base, lli exponent)
  11. {
  12.     lli result=1;
  13.     while(exponent)
  14.     {
  15.         if(exponent & 1)
  16.             result=(result*base)%K;
  17.         exponent>>=1;
  18.         base=(base*base)%K;
  19.     }
  20.     return result%K;
  21. }
  22. int main()
  23. {
  24.     string n;
  25.     cin>>n;
  26.     lli k;
  27.     cin>>k;
  28.     vector<int> position;
  29.     for(int i=0;i<n.length();i++)
  30.         if(n[i]=='5' || n[i]=='0')
  31.             position.push_back(i);
  32.     lli m=0;
  33.     for(int i=0;i<position.size();i++)
  34.         m=(m+power(2,position[i]))%K;
  35.     lli answer=0;
  36.     lli l=n.length();
  37.  
  38. // the following is finding summation via loop
  39.     for(int i=1;i<=k;i++)
  40.         answer=(answer + (power(2,l*(k-i))*m)%K)%K;
  41.     cout<<answer<<endl;
  42.  
  43. // the following finds the sum by using gp formula (1st_term*(ratio^no_of_terms-1)/(ratio-1))    
  44.     answer=1;
  45.     answer=((power(power(2,l),k) - 1)/(power(2,l)-1))%K;
  46.     answer=(answer*m)%K;
  47.     cout<<answer<<endl;
  48.     return 0;
  49. }
Time limit exceeded #stdin #stdout 5s 2900KB
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https://ideone.com/SNQSCH
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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