How to split a string into consecutive substrings of length at most 3 in all possible ways?

Question

I am trying to take a string, between length 1 and 10, and output all possible ways of breaking up the string into consecutive substrings that are of sizes 1, 2, or 3. For example:

Input: 123456

Slice the integer into individual characters, then proceed through to find combinations. The code would return all of the following arrays.

    [1, 2, 3, 4, 5, 6]  
    [12, 3, 4, 5, 6]  
    [1, 23, 4, 5, 6]  
    [1, 2, 34, 5, 6]  
    [1, 2, 3, 45, 6]  
    [1, 2, 3, 4, 56]  
    [12, 34, 5, 6]  
    [12, 3, 45, 6]  
    [12, 3, 4, 56]  
    [1, 23, 45, 6]  
    [1, 2, 34, 56]  
    [1, 23, 4, 56]  
    [12, 34, 56]  
    [123, 4, 5, 6]  
    [1, 234, 5, 6]  
    [1, 2, 345, 6]  
    [1, 2, 3, 456]  
    [123, 456]  
    [1, 23, 456]  
    [1, 234, 56]  
    [12, 345, 6]  
    [12, 3, 456]  
    [123, 4, 56]  
    [123, 45, 6]

I'm trying to do this in ruby. Thanks!

Answer 1

Here's a working function. May be not optimal as I didn't spend much time on it.

str = "1234567890"

def f(s, n)
    return [[]] if s.empty?

    (1..[n, s.length].min).map{|c| f(s[c..-1], n).map{|a| [s[0, c]] + a}}.inject(&:+)
end

puts f(str, 3).collect{|l| l * "\t"}

EDIT: Made it a bit shorter and the length is now passed as second parameter to function for flexibility.

Answer 2

It took me quite a while to figure this out, its a much harder problem then I first though. But eventually I hit upon this solution:

def combinations(s)
  c = (s.length > 3) ? [] : [[s]]
  max = [4, s.length].min
  (1...max).inject(c) do |c, i|
    combinations(s[i..-1]).inject(c) do |c, tail|
      c.push([s[0...i]] + tail)
    end
  end
end

combinations("12345").each { |c| p c }

Produces:

["1", "2", "345"]
["1", "2", "3", "45"]
["1", "2", "3", "4", "5"]
["1", "2", "34", "5"]
["1", "23", "45"]
["1", "23", "4", "5"]
["1", "234", "5"]
["12", "345"]
["12", "3", "45"]
["12", "3", "4", "5"]
["12", "34", "5"]
["123", "45"]
["123", "4", "5"]

Answer 3

Here's another:

class String
  def splitup(prefix=nil)
    parts = []
    if size <= 3
      parts << [prefix,self].compact * ","
    end
    (1..([size,3].min)).each do |p|
      next if p >= size
      parts << slice(p..-1).splitup([prefix,slice(0,p)].compact * ",")
    end
    parts
  end

  def report
    flat = splitup.flatten.sort_by {|x| [-x.size,x]}
    puts
    puts "#{flat.size} permutations of #{self}"
    puts flat
  end
end

and then

>> "123456".report

24 permutations of 123456
1,2,3,4,5,6
1,2,3,4,56
1,2,3,45,6
1,2,34,5,6
1,23,4,5,6
12,3,4,5,6
1,2,3,456
1,2,34,56
1,2,345,6
1,23,4,56
1,23,45,6
1,234,5,6
12,3,4,56
12,3,45,6
12,34,5,6
123,4,5,6
1,23,456
1,234,56
12,3,456
12,34,56
12,345,6
123,4,56
123,45,6
123,456