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  1. #include <stdio.h>
  2. 	#include <stdlib.h>
  3. 	#include <string.h>
  4. 	#include <stdbool.h>
  5. 	#include <math.h>
  6.  
  7. 	#define same_digits(x, y)   num_digits(x) == num_digits(y) ? 1 : 0
  8.  
  9. 	typedef struct arguments {
  10. 		long int min;
  11. 		long int max;
  12. 	} Args;
  13.  
  14. 	short num_digits(long int num) {
  15. 		short count = 0;
  16. 		while (num != 0) {
  17. 			num /= 10;
  18. 			++count;
  19. 		}
  20. 		return count;
  21. 	}
  22.  
  23. 	bool is_palindrome(long int num) {
  24. 		short digits = num_digits(num); 
  25. 		char buffer[digits + 1];
  26. 		sprintf(buffer, "%ld", num);
  27. 		int i;
  28. 		size_t len = strlen(buffer);
  29. 		char *reversed = NULL;
  30. 		reversed = calloc(digits + 1, sizeof(char));
  31. 		for (i = len - 1; i >= 0; i--)
  32. 			reversed[len - 1 - i] = buffer[i];
  33. 		long int new_num;
  34. 		int n = sscanf(reversed, "%ld", &new_num);
  35. 		free(reversed);
  36. 		if (n == 1 && num == new_num) {
  37. 			return true;
  38. 		}
  39. 		return false;
  40. 	}
  41.  
  42. 	void *largest(void *arg) {
  43. 		Args *args = (Args *) arg;
  44. 		long int min = args->min;
  45. 		long int max = args->max;
  46. 		long int i, j;
  47. 		for (i = max; i >= min; i--) {
  48. 			if (is_palindrome(i) == false)
  49. 				continue;
  50. 			int root = (int) sqrt(i);
  51. 			for (j = 2; j <= root; j++) {
  52. 				if (i % j == 0) {
  53. 					if (same_digits(j, (i/j))) {
  54. 						printf("%ld\t*\t%ld\t=\t%ld\n", j, (i/j), i);
  55. 						return NULL;
  56. 					}
  57. 				}
  58. 			}
  59. 		}
  60. 		return NULL;
  61. 	}
  62.  
  63. 	int main(void) {
  64. 		int num;
  65. 		while (fscanf(stdin, "%d", &num) == 1) {
  66. 			if (num == 1) {
  67. 				Args *arguments = NULL;
  68. 				arguments = calloc(1, sizeof(Args));
  69. 				arguments->min = 1;
  70. 				arguments->max = 10;
  71. 				largest((void *) arguments);
  72. 				free(arguments);
  73. 			} else {
  74. 				long int min = pow(10, (num * 2) - 1);
  75. 				long int max = pow(10, (num * 2));
  76. 				Args *args = NULL;
  77. 				args = calloc(1, sizeof(Args));
  78. 				args->min = min;
  79. 				args->max = max;
  80. 				largest((void *) args);
  81. 			}
  82. 		}
  83. 		return EXIT_SUCCESS;
  84. 	}
Success #stdin #stdout 0.26s 9432KB
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stdin
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stdout
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3	*	3	=	9
91	*	99	=	9009
913	*	993	=	906609
9901	*	9999	=	99000099
https://ideone.com/40x3Nn
language:
C (gcc 8.3)
created:
7 years ago
visibility:
public

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