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]

Ok added the arrays will add the code I put which is very wrong/bad/beginner-y as you may see :p — Tal C
– Tal C, Commented Jan 11, 2016 at 9:37
Please make ur question more clear. Give an example if possible. — Harry Bomrah
– Harry Bomrah, Commented Jan 11, 2016 at 9:40
@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? — Stefan
– Stefan, Commented Jan 11, 2016 at 9:42

Community · Accepted Answer · 2017-05-23 12:15:20Z

5

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.

edited May 23, 2017 at 12:15

CommunityBot

11 silver badge

answered Jan 11, 2016 at 10:00

Stefan

115k14 gold badges157 silver badges233 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

sawa · Accepted Answer · 2016-01-11 11:02:51Z

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]

edited Jan 11, 2016 at 11:02

answered Jan 11, 2016 at 10:06

sawa

169k51 gold badges287 silver badges398 bronze badges

2 Comments

Stefan Over a year ago

You might want to explain &.&, it's quite new.

Stefan Over a year ago

Actually, &. is not necessary, because (nil & a) == a evaluates to false == a

ndnenkov · Accepted Answer · 2016-01-11 10:00:44Z

1

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]

edited Jan 11, 2016 at 10:00

answered Jan 11, 2016 at 9:43

ndnenkov

36.2k9 gold badges80 silver badges109 bronze badges

3 Comments

sawa Over a year ago

Why "X" and "Y"?

Stefan Over a year ago

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 Over a year ago

@Stefan, I didn't think it through initially. Now it would be practically copying your answer.

Aleksei Matiushkin · Accepted Answer · 2016-01-11 10:32:14Z

1

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\1/
end
#⇒ 5

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

edited Jan 11, 2016 at 10:32

answered Jan 11, 2016 at 10:23

Aleksei Matiushkin

121k12 gold badges109 silver badges173 bronze badges

2 Comments

Stefan Over a year ago

I like your regex approach, but I'd use /(\w)\1\1/.

Aleksei Matiushkin Over a year ago

@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.)

Harry Bomrah · Accepted Answer · 2016-01-11 10:20:26Z

0

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.

edited Jan 11, 2016 at 10:20

answered Jan 11, 2016 at 10:00

Harry Bomrah

1,6681 gold badge11 silver badges14 bronze badges

4 Comments

Stefan Over a year ago

won? doesn't seem to return anything.

Harry Bomrah Over a year ago

need to pass the board.

Harry Bomrah Over a year ago

@Stefan i missed return statement.

Harry Bomrah Over a year ago

@Stefan But i really like your answer. its really short and sweet.

Collectives™ on Stack Overflow

Check if all strings in one array are in another array

5 Answers 5

Comments

2 Comments

3 Comments

2 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

2 Comments

3 Comments

2 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related