Well I came up with a solution but for bizarre reasons decided to obfu it, so I posted it as Pattern Matching Obfu, you will have to change the string $S as appropriate to your requireements. Your clarification of the constraints on the problem lead to some interesting angles, some that I suspect are unintended. Most especially that irrelevent of the short pattern solution there are likely to be very many long patterns, each of which _ONLY_ match once.

My algorthm, in a rather humourous fashion found the following solutions, amongst many others, that meet your critera in a very short amount of time (the | is the seperator between sub patterns):

bookhelloworldh|ellohellohihell|ohiworldhihello|worldhihelloboo|kpenbo
+okpenworld
bookhelloworldh|ellohellohihell|ohiworldhihello|worldhihellobook|penbo
+okpenworld
bookhelloworldh|ellohellohihell|ohiworldhihello|worldhihellobookp|enbo
+okpenworld
bookhelloworldh|ellohellohihell|ohiworldhihell|oworldhihellobookp|enbo
+okpenworld
bookhelloworldhe|llohellohihell|ohiworldhihello|worldhihellobookp|enbo
+okpenworld
bookhelloworldhel|lohellohihell|ohiworldhihello|worldhihellobookp|enbo
+okpenworld
bookhelloworldhel|lohellohihello|hiworldhihello|worldhihellobookp|enbo
+okpenworld
bookhelloworldhel|lohellohihello|hiworldhihello|worldhihellobook|penbo
+okpenworld
bookhelloworldhel|lohellohihelloh|iworldhihello|worldhihellobook|penbo
+okpenworld
bookhelloworldhell|ohellohihelloh|iworldhihello|worldhihellobook|penbo
+okpenworld
[download]

Yves
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