Check if all strings in one array are in another array

Question

This is for a tic tac toe game. I have an array board with nine string elements, and a nested array WIN_COMBINATIONS with position combinations from board:

board = ["X", "X", "X", " ", " ", " ", " ", " ", " "]
WIN_COMBINATIONS = [
 [0, 1, 2],
 [0, 3, 6],
 [0, 4, 8],
 [3, 4, 5],
 [6, 7, 8],
 [6, 4, 2],
 [1, 4, 7],
 [2, 5, 8]
]

How do I choose the array combinations from board that are all "X" or all "O" using the combinations found in WIN_COMBINATIONS?

For example a different board than the one above in which X wins in the right diagonal.

board = ["X", "O", "X", "O", "X", "O", "X", "X", "O"]
# X | O | X
# ---+---+---
# O | X | O
# ---+---+---
# X | X | O
won?(board) #=> [2,4,6]

• Aleksei Matiushkin: Please provide the examples of these arrays.
• ndnenkov: Give example input-output. Show what you have tried so far.
• Tal C: Ok added the arrays will add the code I put which is very wrong/bad/beginner-y as you may see :p
• Harry Bomrah: Please make ur question more clear. Give an example if possible.
• Stefan: @TalC thanks for adding the arrays, but I still don't understand your last sentence. Could you provide the expected output, i.e. the combinations you want to choose?

Answer 1

A slight variation of ndn's answer:

board = %w(X O X
 O X O
 X X O)
WIN_COMBINATIONS.select { |c| board.values_at(*c).join =~ /XXX|OOO/ }
#=> [[6, 4, 2]]

Explanation:

• select returns all elements for which the block returns true.

• values_at returns the values at the specified indices:

  board.values_at(*[0, 1, 2])
  #=> ["X", "O", "X"]
  

  * converts the array to an argument list, so the above becomes values_at(0, 1, 2)

• join returns a string with the concatenated elements:

  ["X", "O", "X"].join
  #=> "XOX"
  

• =~ checks if the string matches the regular expression /XXX|OOO/, i.e. either XXX or OOO

You can replace select with find if you just want to retrieve the first winning combination.

Answer 2

Edit Code incorporates Stefan's suggestion.

Do this once:

WIN_COMBINATIONS.each(&:sort!)

Then,

h = board.each_index.group_by{|i| board[i]}
# => {"X"=>[0, 1, 2], " "=>[3, 4, 5, 6, 7, 8]}
WIN_COMBINATIONS.find{|a| (h["X"] & a) == a or (h["O"] & a) == a}
# => [0, 1, 2]

• Stefan: You might want to explain &.&, it's quite new.
• Stefan: Actually, &. is not necessary, because (nil & a) == a evaluates to false == a

Answer 3

WIN_COMBINATIONS.find do |combination|
 values_at_positions = board.values_at(*combination).uniq
 values_at_positions.size == 1 and ['X', 'O'].include?(*values_at_positions)
end # => [0, 1, 2]

• sawa: Why "X" and "Y"?
• Stefan: A more straight-forwand (and shorter) check would be values = board.values_at(*combination); values == %w(X X X) || values == %w(O O O)
• ndnenkov: @Stefan, I didn't think it through initially. Now it would be practically copying your answer.

Answer 4

Just out of curiosity (a slightly updated @Stefan’s answer):

WIN_COMBINATIONS.index do |wc|
 board.values_at(*wc).join =~ /(?<l>\w)\k<l>\k<l>/
 # or, as suggested by @Stefan: board.values_at(*wc).join =~ /(\w)1円1円/
end
#⇒ 5

Here we match the combinations to three same symbols, which is likely the most semantically correct interpretation of tic-tac-toe game.

• Stefan: I like your regex approach, but I'd use /(\w)1円1円/.
• Aleksei Matiushkin: @Stefan Indeed, updated, thanks. I left index, though, to make it more flexible (to have a backward connection to WIN_COMBINATIONS array, since it probably makes it easier to debug the wrong values there.)

Answer 5

You can try this.

def won?(board)
 xpos = []
 opos = []
 who_won = nil;
 board.each_with_index{|x,i| xpos << i if x == "X" }
 board.each_with_index{|x,i| xpos << i if x == "O" }
 WIN_COMBINATIONS.each do |com|
 temp = com & xpos
 who_won = "X" if temp == com
 temp = com & opos
 who_won = "O" if temp == com
 break if !who_won.nil?
 end
 return who_won
end
won?(board) #=> X if x wins, O if O wins. nil if no body wins.

Its untested but should work.

• Stefan: won? doesn't seem to return anything.
• Harry Bomrah: need to pass the board.
• Harry Bomrah: @Stefan i missed return statement.
• Harry Bomrah: @Stefan But i really like your answer. its really short and sweet.