nqueen.py

def solve_n_queens(n):
    def is_safe(board, row, col):
      
        for i in range(row):
            if board[i] == col or \
               board[i] - i == col - row or \
               board[i] + i == col + row:
                return False
        return True

    def solve_nq_util(board, row):
       
        if row >= n:
            result.append(board[:])
            return

       
        for col in range(n):
            if is_safe(board, row, col):
                board[row] = col 
                solve_nq_util(board, row + 1)  
                board[row] = -1 

    
    result = []
  
    board = [-1] * n
    solve_nq_util(board, 0)
    return result


n = 4
solutions = solve_n_queens(n)
for solution in solutions:
    print("Solution:")
    for i in range(n):
        row = ['.'] * n
        row[solution[i]] = 'Q'
        print(" ".join(row))
    print()