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  1. #include <stdio.h>
  2.  
  3.  
  4. /* Potęgowanie w integerach: https://e...content-available-to-author-only...a.org/wiki/Exponentiation_by_squaring*/
  5. unsigned long pow(unsigned long a, unsigned long b) {
  6. 	if (b == 0) return 1;
  7. 	if (b == 1) return a;
  8. 	if (b % 2 == 0) return pow(a * a, b / 2);
  9. 	else return a * pow(a * a, (b - 1) / 2);
  10. 	}
  11.  
  12.  
  13. /* Suma cyfr w liczbie, prosta obserwacja: kolejne cyfry liczby n to (od prawej):
  14.  * n % 10 
  15.  * n / 10 % 10
  16.  * n / 100 % 10 
  17.  * .....
  18.  */ 
  19. unsigned long sum_digits(unsigned long n){
  20. 	unsigned long s = 0;
  21. 	for (unsigned long i = 0; n / pow(10, i) > 0; ++i)
  22. 		s += (n / pow(10, i)) % 10;
  23. 	return s; 
  24. 	}
  25.  
  26.  
  27.  
  28. /* Proste, rekurencyjne wywoływanie sumy cyfr, aż do 
  29.  * przypadku bazowego: liczba jednocyfrowej, 
  30.  * wtedy n / 10 == 0
  31.  * */
  32. unsigned long sum_digits_until_one(unsigned long n) {
  33. 	if (n / 10 == 0) return n;
  34. 	else 
  35. 		return sum_digits_until_one(sum_digits(n));
  36. 	}
  37.  
  38.  
  39. int main(int argc, char **argv)
  40. {
  41. 	printf("%d \n", sum_digits_until_one(98792) == 8); // -> 1 (true)
  42. 	printf("%d \n", sum_digits_until_one(6841) == 1); // -> 1 (true)
  43. 	printf("%d \n", sum_digits_until_one(7777) == 1); // -> 1 (true)
  44. 	printf("%d \n", sum_digits_until_one(12345678) == 9); // -> 1 (true)
  45. 	printf("%d \n", sum_digits_until_one(90009093) == 3); // -> 1 (true)
  46. 	printf("%d \n", sum_digits_until_one(21111111111) == 3); // -> 1 (true)
  47. 	printf("-----------------------------------------------------------\n");
  48. 	printf("%lu \n", sum_digits_until_one(98792)); // -> 8 (true)
  49. 	printf("%lu \n", sum_digits_until_one(6841)); // -> 1 (true)
  50. 	printf("%lu \n", sum_digits_until_one(7777)); // -> 1 (true)
  51. 	printf("%lu \n", sum_digits_until_one(12345678)); // -> 9 (true)
  52. 	printf("%lu \n", sum_digits_until_one(90009093)); // -> 3 (true)
  53. 	printf("%lu \n", sum_digits_until_one(21111111111)); // -> 3 (true)
  54. 	return 0;
  55. }
Success #stdin #stdout 0s 4520KB
comments (?)
stdin
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Standard input is empty
stdout
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1 
1 
1 
1 
1 
1 
-----------------------------------------------------------
8 
1 
1 
9 
3 
3
https://ideone.com/vNJwPE
language:
C (gcc 8.3)
created:
6 years ago
visibility:
public

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