n-queen

8queen.py

class QueenN():
    def __init__(self):
        pass

    def create(self, n):
        boards = [[-1] * n]
        for row in range(n):
            boards = self.add_row(row, n, boards)

        print n, "Pattern:", len(boards)
        for board in boards:
            for col in board:
                for i in xrange(n):
                    if i == col:
                        print "Q",
                    else: 
                        print "_",
                print 
            print 


    def add_row(self, row, n, boards):
        next_boards = []
        for board in boards:
            for col in range(n):
                array = board[:]
                if self.is_safe(board, row, col):
                    array[row] = col
                    next_boards.append(array)

        return next_boards

    def is_safe(self, board, row, col):
        # cols
        if col in board:
            return False

        # x
        for i in range(row):
            if (i - board[i]) == (row - col):
                return False
            if abs(board[i] + i) == (row + col):
                return False
        return True
      

if __name__ == '__main__':
    queen = QueenN()
    for i in range(3, 9):
        queen.create(i)

3 Pattern: 0
4 Pattern: 2
5 Pattern: 10
6 Pattern: 4
7 Pattern: 40
8 Pattern: 92
[Finished in 0.6s]