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  1. #include <stdio.h>
  2. #include <stdbool.h>
  3. #include <stdlib.h>			/* calloc(), free(), abs(), exit(), ... */
  4. #include <limits.h>			/* LONG_MAX */
  5.  
  6. /* safer free() ---------------------- */
  7. #define FREE(p)				\
  8. 	do{				\
  9. 		if ( (p) ) {		\
  10. 			free( (p) );	\
  11. 			(p) = NULL;	\
  12. 		}			\
  13. 	}while(0)
  14.  
  15. /* safer fclose() -------------------- */
  16. #define FCLOSE(fp)			\
  17. 	do {				\
  18. 		if ( (fp) ) {		\
  19. 			fclose((fp));	\
  20. 			(fp) = NULL;	\
  21. 		}			\
  22. 	}while(0)
  23.  
  24. typedef struct MinSum0Pair {
  25. 	long int small, large;
  26. } MinSum0Pair;
  27.  
  28. /* --------------------------------------------------------------
  29.  * Create buffer 'buf' and fill-it up with the contents of the file 'fname'.
  30.  * Return the length of the buffer, or 0 on error.
  31.  * --------------------------------------------------------------
  32.  */
  33. long int buffer_make_fromfile( long int **buf, const char *fname )
  34. {
  35. 	FILE *fp = NULL;
  36. 	long int i, buflen = 0;
  37.  
  38. 	if ( !fname || !buf ) {
  39. 		puts( "*** error: invalid pointer!" );
  40. 		goto ret_failure;
  41. 	}
  42.  
  43. 	/* open input file */
  44. 	if ( NULL == (fp=fopen(fname, "r")) ) {
  45. 		puts( "*** error: cannot open input file!" );
  46. 		goto ret_failure;
  47. 	}
  48.  
  49. 	/* get the 1st number (buflen) and allocate so many long ints, in buf */
  50. 	if ( 1 != fscanf(fp, "%ld", &buflen) ) {
  51. 		puts( "*** error: fscanf() failed!" );
  52. 		goto ret_failure;
  53. 	}
  54. 	if ( NULL == (*buf=calloc(buflen, sizeof(long int)) ) ) {
  55. 		puts( "*** error: out of memory!" );
  56. 		goto ret_failure;
  57. 	}
  58.  
  59. 	/* fill-in the buffer with the rest of long ints */
  60. 	for (i=0; !feof(fp) && 1 == fscanf(fp, "%ld", &(*buf)[i]); i++ )
  61. 		; /* void */
  62.  
  63. 	FCLOSE(fp);
  64. 	return buflen;
  65.  
  66. ret_failure:
  67. 	FCLOSE(fp);
  68. 	return 0;
  69. }
  70.  
  71. /* --------------------------------------------------------------
  72.  * Print the first 'maxlen' elements of the buffer 'buf', separated be a space char.
  73.  * --------------------------------------------------------------
  74.  */
  75. void buffer_print( long int buf[], long int maxlen )
  76. {
  77. 	long int i = 0;
  78. 	for (; i < maxlen; i++ )
  79. 		printf( "%ld ", buf[i] );
  80. 	puts("\b");
  81.  
  82. 	return;
  83. }
  84.  
  85. /* --------------------------------------------------------------
  86.  * Find in buffer 'buf' (of length 'buflen') the pair of values
  87.  * whose sum is closest to 0, and store them in '*pair'.
  88.  * Return false on error, true otherwise.
  89.  *
  90.  * Alg: Indexers 'istart' & 'iend' traverese 'buf' simultaneously, starting from its
  91.  *	edges. Until they meet, they keep track of the minimum sum of pairs, along with
  92.  * 	the indicies that correspond to the members of the min pair ('ismall' & 'ilarge').
  93.  * --------------------------------------------------------------
  94.  */
  95. bool pair_minsum0( MinSum0Pair *pair, const long int buf[], long int buflen )
  96. {
  97. 	long int sum, minsum = LONG_MAX;		/* current & minimum sums      */
  98. 	long int istart = 0, iend = buflen - 1;		/* array indexers (start & end)*/
  99. 	long int ismall = istart, ilarge = iend;	/* pair's small & large indicies*/
  100.  
  101. 	if ( !pair || !buf ) {
  102. 		puts( "*** error: invalid pointer!" );
  103. 		goto ret_failure;
  104. 	}
  105. 	if ( buflen < 2 ) {
  106. 		puts("*** error: insufficient data (must be more than 2 numbers)!");
  107. 		goto ret_failure;
  108. 	}
  109.  
  110. 	/* traverse the buffer simultaneously from both edges */
  111. 	while ( istart < iend )
  112. 	{
  113. 		sum = buf[ istart ] + buf[ iend ];
  114.  
  115. 		/* get new minimum sum (if any) and update accordingly ismall & ilarge */
  116. 		if ( abs(sum) < abs(minsum) )
  117. 		{
  118. 			minsum = sum;
  119. 			ismall = istart;
  120. 			ilarge = iend;
  121. 		}
  122. 		if ( sum < 0 )
  123. 			istart++;
  124. 		else
  125. 			iend--;
  126. 	}
  127.  
  128. 	pair->small = buf[ ismall ];
  129. 	pair->large = buf[ ilarge ];
  130.  
  131. 	return true;
  132.  
  133. ret_failure:
  134. 	return false;
  135. }
  136.  
  137. /* --------------------------------------------------------------
  138.  *
  139.  * --------------------------------------------------------------
  140.  */
  141. int main( void )
  142. {
  143. 	char 		fname[] = "op2.in";
  144. 	long int 	*buf 	= NULL;
  145. 	long int 	buflen 	= 0;
  146. 	MinSum0Pair	pair 	= { 0L, 0L };
  147.  
  148. 	/* read input-file contents into our buffer */
  149. 	buflen = buffer_make_fromfile( &buf, fname );
  150. 	if ( 0 == buflen )
  151. 		goto ret_failure;
  152. 	buffer_print( buf, buflen );
  153.  
  154. 	/* find & store the pair whose sum is closest to 0 */
  155. 	if ( !pair_minsum0( &pair, buf, buflen) )
  156. 		goto ret_failure;
  157.  
  158. 	printf( "%ld %ld\n", pair.small, pair.large );
  159.  
  160. 	FREE(buf);
  161. 	exit( EXIT_SUCCESS );
  162.  
  163. ret_failure:
  164. 	FREE(buf);
  165. 	exit( EXIT_FAILURE );
  166. }
  167.  
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https://ideone.com/Oq8aL
language:
C (gcc 8.3)
created:
13 years ago
visibility:
secret

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