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  1. // C++ Program to implement
  2. // the above approach
  3. #include <bits/stdc++.h>
  4. #define ll long long int
  5. using namespace std;
  6.  
  7. // Function to find a^b modulo M
  8. ll modPower(ll a, ll b, ll M)
  9. {
  10.     ll res = 1;
  11.     while (b) {
  12.         if (b & 1)
  13.             res = res * a % M;
  14.         a = a * a % M;
  15.         b >>= 1;
  16.     }
  17.     return res;
  18. }
  19.  
  20. // Function to find the first and last
  21. // M digits from N^K
  22. void findFirstAndLastM(ll N, ll K, ll M)
  23. {
  24.     // Calculate Last M digits
  25.     ll lastM
  26.         = modPower(N, K, (1LL) * pow(10, M));
  27.  
  28.     // Calculate First M digits
  29.     ll firstM;
  30.  
  31.     double y = (double)K * log10(N * 1.0);
  32.  
  33.     // Extract the number after decimal
  34.     y = y - (ll)y;
  35.  
  36.     // Find 10 ^ y
  37.     double temp = pow(10.0, y);
  38.  
  39.     // Move the Decimal Point M - 1 digits forward
  40.     firstM = temp * (1LL) * pow(10, M - 1);
  41.  
  42.     // Print the result
  43.     cout << firstM << " ";
  44.     string s = to_string(lastM);
  45.     int t = M - s.size();
  46.     while(t--)
  47.     {
  48.         cout<<0;
  49.     }
  50.     cout<<lastM<<endl;
  51.  
  52. }
  53.  
  54. // Driver Code
  55. int main()
  56. {
  57.     ll N = 12, K = 12, M = 4;
  58.     cin>>N>>K>>M;
  59.  
  60.     findFirstAndLastM(N, K, M);
  61.     return 0;
  62. }
  63.  
Success #stdin #stdout 0s 5596KB
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https://ideone.com/xCKB54
Find the first and last M digits from K-th power of N
language:
C++14 (gcc 8.3)
created:
2 years ago
visibility:
public

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