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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. #define int long long
  6.  
  7. int n_digs;
  8. int pow_sum[10];
  9. int pows[10];
  10.  
  11. int between(int a,int b,int a_digs,int n)
  12. {
  13.     int k=n_digs-a_digs;
  14.     int ret=pow_sum[k-1];
  15.     a*=pows[k];
  16.     b*=pows[k];
  17.     ret+=max(0ll,min(n+1,b)-a);
  18.     return ret;
  19. }
  20.  
  21. main()
  22. {
  23.     int n,k;
  24.     cin>>n>>k;
  25.     n_digs=1+log10(n);
  26.  
  27.     pows[1]=pow_sum[1]=10;
  28.     for(int i=2;i<10;i++)
  29.     {
  30.         pows[i]=10*pows[i-1];
  31.         pow_sum[i]=pows[i]+pow_sum[i-1];
  32.     }
  33.  
  34.  
  35.     int c_ord=1;
  36.     int c_num=1;
  37.     int c_dig=1;
  38.     while(c_ord<k)
  39.     {
  40.         int n_ord=c_ord+1+between(c_num,c_num+1,c_dig,n);
  41.         if(n_ord<=k)
  42.         {
  43.             c_num++;
  44.             c_ord=n_ord;
  45.         }
  46.         else
  47.         {
  48.             c_num*=10;
  49.             c_ord++;
  50.             c_dig++;
  51.         }
  52.     }
  53.     cout<<c_num<<endl;
  54. }
  55.  
Success #stdin #stdout 0s 3344KB
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stdout 
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https://ideone.com/AzW0PP
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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