Combine multiple strings in array 1 to form array 2

Question

I have an array of strings "A" and a target string "B". The B string contains only characters from a to z and does not contain spaces. I need a ruby function that returns the array of strings which represents all possible ways to form B from elements of Array A. The order in which combinations are returned is irrelevant. Words from A can be used multiple times.

Example:

A = [‘x’, ‘y’, ‘z’, 'yz',‘xy’, ‘xyz’] 

B = ‘xyz’ 

method(A, B) => [x y z, x yz, xyz, xy z]

I looked into permutation method but can't get it to work.

Could you provide an example of what've tried so far, and if possible an example of what the output should look like? — fmendez
– fmendez, Commented Oct 3, 2013 at 21:38
A = [‘x’, ‘y’, ‘z’, ‘yy’, ‘yz’] B = ‘xyyz’ method_name(A, B) => [‘x y yz’, ‘xy yz’, etc] Ive tried scanning and mapping - so frustrating! Im new to Ruby and I always have such a hard time. — piratebroadcast
– piratebroadcast, Commented Oct 3, 2013 at 21:55

Matt · Accepted Answer · 2013-10-03 22:33:13Z

1

Here's a recursive solution that doesn't iterate through the permutations:

def find_possible_combinations( list, str )
  list.select { |a| str.start_with? a }.map do |a|
    if a == str
      [a]
    else
      find_possible_combinations( list-[a], str.slice(a.length..-1) )
        .map { |c| "#{a} #{c}" }
    end
  end.flatten
end

puts "#{find_possible_combinations( %w( x y z yz xy xyz ), 'xyz' )}"

Output:

["x y z", "x yz", "xy z", "xyz"]

answered Oct 3, 2013 at 22:33

Matt

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Comments

Cary Swoveland · Accepted Answer · 2013-10-04 21:51:32Z

0

A = %w[x y z yz xy xyz] 
B = "xyz"
SIZE = B.size

def combos
  (1..SIZE).inject([]) {|c, n| c.concat(combos_by_size(n))}.reject(&:empty?)
end

# Select all combinations of size n having SIZE characters
def combos_by_size(n)
  A.combination(n).to_a.inject([]) {|c, a| c.concat(matching_combos(a)) if a.join.size == SIZE; c}.reject(&:empty?)
end


# Select all matching combinations using all elements of array a
def matching_combos(a)
  a.permutation.to_a.select {|p| p.join == B}
end

combos # => [["xyz"], ["x", "yz"], ["xy", "z"], ["x", "y", "z"]]

edited Oct 4, 2013 at 21:51

answered Oct 4, 2013 at 4:54

Cary Swoveland

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