Problem of placing N chess queens on an N×N chessboard so that no two queens attack each other (https://www.geeksforgeeks.org/backtracking-set-3-n-queen-problem/)

Backtracking : N Queens.py

#!/usr/bin/env python3


def is_safe(row, col, size, board):
	# check vertical
	for y in range(row):
		if board[y][col]:
			return False

	# check left diagonal
	for x, y in zip(range(col - 1, -1, -1), range(row - 1, -1, -1)):
		if board[y][x]:
			return False

	# check right diagonal
	for x, y in zip(range(col + 1, size), range(row - 1, -1, -1)):
		if board[y][x]:
			return False

	return True


def n_queens(row, size, board):
	if row == size:
		for strip in board:
			for bool in strip:
				if bool:
					print('x ', end='')
				else:
					print('o ', end='')
			print()
		print()

		return True

	for col in range(size):
		if is_safe(row, col, size, board):
			board[row][col] = True
			n_queens(row + 1, size, board)
			board[row][col] = False

	return False


def main():
	n = 8
	board = [[False for i in range(n)] for j in range(n)]

	n_queens(0, n, board)


if __name__ == '__main__':
	main()