gistfile1.txt

Haystack: babaacb
Needle: abab

Split into [ "babaa", "b" ]

> Match the longest substring with the input and keep track of the longest match.
> If you don't get a complete match, use the longest one to slice up the
> substring once more, and retry with the next longest substring.

There's no complete match, and the longest match is "bab". So splice up the substring again, and retry with
[ "bab", "aa", "b" ].

"bab" matches, but then the left subproblem is unsolvable: The haystack part [] cannot match the needle part "a".

Now what??