senior sem actual code.py

"""The n Rook puzzle"""
class NQueens:
     """Generate all valid solutions for the n rooks puzzle"""
     def __init__(self, size):
         # Store the puzzle (problem) size and the number of valid solutions
         self.size = size
         self.solutions = 0
         self.solve()
 
     def solve(self):
         """Solve the n queens puzzle and print the number of solutions"""
         positions = [-1] * self.size
         self.put_queen(positions, 0)
         print("Found", self.solutions, "solutions.")
 
     def put_queen(self, positions, target_row):
         """
         Try to place a queen on target_row by checking all N possible cases.
         If a valid place is found the function calls itself trying to place a queen
         on the next row until all N queens are placed on the NxN board.
         """
         # Base (stop) case - all N rows are occupied
         if target_row == self.size:
             self.show_full_board(positions)
             self.solutions += 1
         else:
             # For all N columns positions try to place a queen
             for column in range(self.size):
                 # Reject all invalid positions
                 if self.check_place(positions, target_row, column):
                     positions[target_row] = column
                     self.put_queen(positions, target_row + 1)
 
     def check_place(self, positions, ocuppied_rows, column):
         """
         Check if a given position is under attack from any of
         the previously placed queens (check column and diagonal positions)
         """
         for i in range(ocuppied_rows):
             if positions[i] == column or \
                 positions[i] - i == column - ocuppied_rows or \
                 positions[i] + i == column + ocuppied_rows:
 
                 return False
         return True
 
     def show_full_board(self, positions):
         """Show the full NxN board"""
         for row in range(self.size):
             line = ""
             for column in range(self.size):
                 if positions[row] == column:
                     line += "Q "
                 else:
                     line += ". "
             print(line)
         print("\n")
def main():
    """Initialize and solve the n queens puzzle"""
    NQueens(8)
    if __name__ == "__main__":
        # execute only if run as a script
        main()