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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <string.h>
  4. #include <math.h>
  5.  
  6. int const max = 'Z'-'A' + 1;
  7.  
  8. static char const*
  9. encode(char* buf, size_t bufsize, int n) {
  10. 	char* beg = buf;
  11. 	char* cur = buf+bufsize-1;
  12.  
  13. 	*beg = *cur = '\0';
  14.  
  15. 	while (n > 0 && cur > beg) {
  16. 		int r = (n%max);
  17. 		if (r == 0) {
  18. 			n /= max*2;
  19. 			r = max;
  20. 		} else
  21. 			n /= max;
  22. 		*(--cur) = 'A'-1+r;
  23. 	}
  24. 	return cur;
  25. }
  26.  
  27. static int
  28. decode(char const* str) {
  29. 	char const* beg = str;
  30. 	char const* end = beg+strlen(str)-1;
  31. 	int n = 0;
  32.  
  33. 	while (beg < end) {
  34. 		n += pow(max, end-beg) * (*beg-'A'+1);
  35. 		++beg;
  36. 	}
  37. 	n += ((*end)-'A'+1);
  38. 	return n;
  39. }
  40.  
  41. int
  42. main(int argc, char* argv[]) {
  43. 	char buf[10];
  44.  
  45. 	printf("decode value: '%s' -> %d\n", "A", decode("A"));
  46. 	printf("decode value: '%s' -> %d\n", "Z", decode("Z"));
  47. 	printf("decode value: '%s' -> %d\n", "AA", decode("AA"));
  48. 	printf("decode value: '%s' -> %d\n", "DBA", decode("DBA"));
  49.  
  50. 	printf("encode value: %d -> '%s'\n", 2757, encode(buf, sizeof buf, 2757));
  51. 	printf("encode value: %d -> '%s'\n", 125, encode(buf, sizeof buf, 125));
  52.  
  53. 	return 0;
  54. }
  55.  
Success #stdin #stdout 0s 2008KB
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stdin
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Standard input is empty
stdout
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decode value: 'A' -> 1
decode value: 'Z' -> 26
decode value: 'AA' -> 27
decode value: 'DBA' -> 2757
encode value: 2757 -> 'DBA'
encode value: 125 -> 'DU'
https://ideone.com/WlYyoS
language:
C (gcc 8.3)
created:
9 years ago
visibility:
public

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