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  1. N = 4
  2.  
  3. # Function to print the solution board
  4. def print_board(board):
  5.     for row in board:
  6.         print(row)
  7.     print()
  8.  
  9. # Check if a queen can be safely placed at board[row][col]
  10. def is_safe(board, row, col):
  11.     # Check same column
  12.     for i in range(row):
  13.         if board[i][col] == 1:
  14.             return False
  15.  
  16.     # Check upper-left diagonal
  17.     i, j = row - 1, col - 1
  18.     while i >= 0 and j >= 0:
  19.         if board[i][j] == 1:
  20.             return False
  21.         i -= 1
  22.         j -= 1
  23.  
  24.     # Check upper-right diagonal
  25.     i, j = row - 1, col + 1
  26.     while i >= 0 and j < N:
  27.         if board[i][j] == 1:
  28.             return False
  29.         i -= 1
  30.         j += 1
  31.  
  32.     return True
  33.  
  34. # Backtracking function to solve N-Queen
  35. def solve(board, row, solutions):
  36.     # Base case: if all queens are placed (row == N), save the solution
  37.     if row == N:
  38.         # Save a deep copy of the board as a solution
  39.         solutions.append([row[:] for row in board]) 
  40.         return
  41.  
  42.     # Try placing the queen in each column of the current row
  43.     for col in range(N):
  44.         if is_safe(board, row, col):
  45.             board[row][col] = 1 # Place queen
  46.  
  47.             # Recurse to place the queen in the next row
  48.             solve(board, row + 1, solutions)
  49.  
  50.             # Backtrack: remove the queen (reset to 0) before trying the next column
  51.             board[row][col] = 0 
  52.  
  53. # Main driver code
  54. # Initialize an empty N x N board (4x4 in this case)
  55. board = [[0] * N for _ in range(N)] 
  56. solutions = []
  57. solve(board, 0, solutions)
  58.  
  59. # Print all found solutions
  60. count = 1
  61. for sol in solutions:
  62.     print("Solution", count)
  63.     for row in sol:
  64.         print(row)
  65.     print()
  66.     count += 1
Success #stdin #stdout 0.08s 14176KB
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Solution 1
[0, 1, 0, 0]
[0, 0, 0, 1]
[1, 0, 0, 0]
[0, 0, 1, 0]

Solution 2
[0, 0, 1, 0]
[1, 0, 0, 0]
[0, 0, 0, 1]
[0, 1, 0, 0]
https://ideone.com/5v9HC5
language:
Python 3 (python  3.12)
created:
4 days ago
visibility:
public

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