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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <stdint.h>
  4.  
  5. int n;	// MAX = 16
  6. int solution_count = 0;
  7. int solution_count_half = 0;
  8. int solution_count_center = 0;
  9. uint32_t col=0, asc=0, desc=0;
  10.  
  11.  
  12. bool bCenter=false;
  13. void backtrack(int i) 
  14. {
  15. 	int max = n;
  16. 	if (i==0) max = (n+1)/2;
  17.  
  18.     if(i == n) {
  19. 		if (bCenter)
  20. 			solution_count_center++;
  21. 		else
  22. 	        solution_count_half++;
  23.         return;
  24.     }
  25.     uint32_t mc, md, ma;
  26.     for(int j=0; j != max; j++) {
  27. 		if (i==0 && (n%2)==1 && j==max-1)
  28. 			bCenter=true;
  29.     	if (col & (mc = 1<<j)) continue;
  30.     	if (desc & (md = 1 << (i+j))) continue;
  31.     	if (asc & (ma = 1 << (15+i-j))) continue;
  32.     	uint32_t oldc = col, oldd = desc, olda = asc;
  33.         col |= mc;
  34.         desc |= md;
  35.         asc |= ma;
  36.         backtrack(i+1);
  37.         col = oldc;
  38.         desc = oldd;
  39.         asc = olda;
  40.     }
  41. }
  42.  
  43. int main() 
  44. { 
  45. 	n=14;
  46.  
  47. 	backtrack(0);
  48. 	if (n % 2 == 0)
  49. 		solution_count = solution_count_half * 2;
  50. 	else
  51. 		solution_count = solution_count_half * 2 + solution_count_center;
  52. 	printf("%d\n", solution_count);
  53.  
  54. 	return 0;
  55. }
  56.  
Success #stdin #stdout 1.46s 3460KB
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https://ideone.com/9oJkhI
N-queen, Improvement using mirror
language:
C++ (gcc 8.3)
created:
9 years ago
visibility:
public

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