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  1. #include <stdio.h>
  2.  
  3. /* Potęgowanie w integerach: https://e...content-available-to-author-only...a.org/wiki/Exponentiation_by_squaring*/
  4. unsigned long pow(unsigned long a, unsigned long b) {
  5.     if (b == 0) return 1;
  6.     if (b == 1) return a;
  7.     if (b % 2 == 0) return pow(a * a, b / 2);
  8.     else return a * pow(a * a, (b - 1) / 2);
  9.     }
  10.  
  11. /* Suma cyfr w liczbie, prosta obserwacja: kolejne cyfry liczby n to (od prawej):
  12.  * n % 10 
  13.  * n / 10 % 10
  14.  * n / 100 % 10 
  15.  * .....
  16.  */ 
  17. unsigned long sum_digits(unsigned long n){
  18.     unsigned long s = 0;
  19.     for (unsigned long i = 0; n / pow(10, i) > 0; ++i)
  20.         s += (n / pow(10, i)) % 10;
  21.     return s; 
  22.     }
  23.  
  24. /* Proste, rekurencyjne wywoływanie sumy cyfr, aż do 
  25.  * przypadku bazowego: liczba jednocyfrowej, 
  26.  * wtedy n / 10 == 0
  27.  * */
  28. unsigned long sum_digits_until_one(unsigned long n) {
  29.     if (n / 10 == 0) return;
  30.     else 
  31.         return sum_digits_until_one(sum_digits(n));
  32.     }
  33.  
  34. int main(int argc, char **argv)
  35. {
  36.     printf("%lu \n", sum_digits_until_one(98792) == 8); // -> 1 (true)
  37.     printf("%lu \n", sum_digits_until_one(6841) == 1); // -> 1 (true)
  38.     return 0;
  39. }
Success #stdin #stdout 0s 4388KB
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https://ideone.com/mBr4Nl
language:
C (gcc 8.3)
created:
6 years ago
visibility:
public

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