Just for kicks, here's what the solution looks like in the Haskell programming language:

combos n ls = filter ((>= n) . length)
            . map concat
            . sequence
            . map (([]:) . map return)
            $ ls
[download]

(This is analogous to the Perl solution provided by hv earlier.)

Examples:

> combos 1 ["abc", "def"]
["d","e","f","a","ad","ae","af","b","bd","be","bf","c","cd","ce","cf"]
[download]

Here's the (elided) answer to your example question:

> combos 4 ["abc", "de", "fgh", "i", "jk", "l", "m"]
["ijlm","iklm","fjlm","fklm","film","fijm", ...
 "cehijlm","cehik","cehikm","cehikl","cehiklm"]
[download]

Cheers,
Tom

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.