8queens

import copy

SIZE = 8
numSolutions = 0

board = {'numQueens': 0} # keys are (x, y), values are 'Q', '.', 'x'

QUEEN = 'Q'
EMPTY = '.'

def placeQueen(board):
    board = copy.copy(board)
    for y in range(SIZE):
        for x in range(SIZE):
            canPlaceQueenHere = True
            # Check all the under-attack positions for existing queens:
            for column in range(SIZE): # Check the row of (x, y)
                if board.get((column, y), EMPTY) == QUEEN:
                    canPlaceQueenHere = False

            for row in range(SIZE): # Check the column of (x, y)
                if board.get((x, row), EMPTY) == QUEEN:
                    canPlaceQueenHere = False

            for diagonalOffset in range(1, SIZE): # Check the diagonals of (x, y)
                if board.get((x + diagonalOffset, y + diagonalOffset), EMPTY) == QUEEN:
                    canPlaceQueenHere = False
                if board.get((x - diagonalOffset, y - diagonalOffset), EMPTY) == QUEEN:
                    canPlaceQueenHere = False
                if board.get((x + diagonalOffset, y - diagonalOffset), EMPTY) == QUEEN:
                    canPlaceQueenHere = False
                if board.get((x - diagonalOffset, y + diagonalOffset), EMPTY) == QUEEN:
                    canPlaceQueenHere = False

            if canPlaceQueenHere:
                # Placing the queen on the board:
                board[(x, y)] = QUEEN
                board['numQueens'] += 1

                if board['numQueens'] == SIZE:
                    printBoard(board)
                else:
                    placeQueen(board) # RECURSIVE CASE

                # Undo this most recent queen placement:
                board[(x, y)] = EMPTY
                board['numQueens'] -= 1
    return # BASE CASE


def printBoard(board):
    for y in range(SIZE):
        for x in range(SIZE):
            space = board.get((x, y), EMPTY)
            print(space + ' ', end='')
        print()
    print()

placeQueen(board)