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  1. #include <stdio.h>
  2. #include <math.h> // for abs() function
  3.  
  4. // Function to check if a queen can be placed at position x[k]
  5. int place(int x[], int k) {
  6.     for (int i = 1; i < k; i++) {
  7.         if ((x[i] == x[k]) || (abs(x[i] - x[k]) == abs(i - k)))
  8.             return 0;
  9.     }
  10.     return 1;
  11. }
  12.  
  13. // Backtracking function to solve the N-Queens problem
  14. int nqueens(int n) {
  15.     int x[20]; // max board size set to 20
  16.     int k = 1, count = 0;
  17.     x[k] = 0;
  18.  
  19.     while (k != 0) {
  20.         x[k]++;
  21.         while ((x[k] <= n) && (!place(x, k)))
  22.             x[k]++;
  23.  
  24.         if (x[k] <= n) {
  25.             if (k == n) {
  26.                 printf("\nSolution %d\n", ++count);
  27.                 for (int i = 1; i <= n; i++) {
  28.                     for (int j = 1; j <= n; j++) {
  29.                         printf("%c ", (j == x[i]) ? 'Q' : 'X');
  30.                     }
  31.                     printf("\n");
  32.                 }
  33.             } else {
  34.                 k++;
  35.                 x[k] = 0;
  36.             }
  37.         } else {
  38.             k--; // backtrack
  39.         }
  40.     }
  41.  
  42.     return count;
  43. }
  44.  
  45. // Main function
  46. int main() {
  47.     int n;
  48.     printf("Enter the size of chessboard: ");
  49.     scanf("%d", &n);
  50.     printf("\nThe number of possibilities are %d\n", nqueens(n));
  51.     return 0;
  52. }
  53.  
Success #stdin #stdout 0.01s 5320KB
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stdout
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Enter the size of chessboard: 
Solution 1
X Q X X 
X X X Q 
Q X X X 
X X Q X 

Solution 2
X X Q X 
Q X X X 
X X X Q 
X Q X X 

The number of possibilities are 2
https://ideone.com/Bek9mX
language:
C (gcc 8.3)
created:
3 days ago
visibility:
public

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