Re: [Pharo-users] how to use indexes to copy a substring out of a string

[Roelof Wobben via Pharo-users]

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Thanks Ben, I think you almost give me the answer but I have to do some testing to see how it really works, Roelof Op 30-12-2018 om 02:14 schreef Ben Coman: On Sun, 30 Dec 2018 at 00:29, Roelof Wobben <r.wob...@home.nl> wrote: Hello, Still working on AdventOfCode I'm struggling to see how this can be solved. Now, a nice string is one with all of the following properties: It contains a pair of any two letters that appears at least twice in the string without overlapping, like xyxy (xy) or aabcdefgaa (aa), but not like aaa (aa, but it overlaps). To exclude overlaps, one approach could be to subtract each candidate pair from the string  and then check the remainder-string for matches. I'm not sure, but suspect that as the candidate pair progresses through the string, only the  trailing remainder-string needs matching since the preceding remainder-string has already been checked. So a Pharo 7 Spotter search for 'pairs' finds 28 implementors  where SequenceableCollection>>overlappingPairsCollect: looks quite close to what is required...   'abcdefg' asArray overlappingPairsCollect: [ :a :b | { a.b } ].  "#(   #($a $b)    #($b $c)    #($c $d)    #($d $e)    #($e $f)    #($f $g))"  Reviewing its implementation...     SequenceableCollection>>overlappingPairsCollect: aBlock  | retval | retval := self species ofSize: self size - 1. 1 to: self size - 1 do: [:i | retval at: i put: (aBlock value: (self at: i) value: (self at: i + 1)) ]. ^retval it can be adapted to provide also a remainder...     SequenceableCollection>>overlappingPairsRemainderCollect: aBlock  | retval | retval := self species ofSize: self size - 1. 1 to: self size - 1 do: [:i | retval at: i put: (aBlock value: (self at: i) value: (self at: i + 1) value: (self allButFirst: i + 1)) ]. ^retval for use like this...   'abcdefg' asArray  overlappingPairsRemainderCollect: [ :a :b :rem | { a.b.rem } ] "#(   #($a $b #($c $d $e $f $g))    #($b $c #($d $e $f $g))    #($c $d #($e $f $g))    #($d $e #($f $g))    #($e $f #($g))    #($f $g #()))"  It contains at least one letter which repeats with exactly one letter between them, like xyx, abcdefeghi (efe), or even aaa. You might adapt "overlappingPairsCollect: aBlock" into  "overlappingPairsSkip: n collect: aBlock" but changing  "size -1"  and   "i + 1" into  "size - n"  and   "i + n"   HTH cheers -ben P.S. If  #overlappingPairsSkip:collect:  seemed generically useful to push into Pharo, then the following would be redefined to reuse it...   SequenceableCollection>>overlappingPairsCollect: aBlock       ^self overlappingPairsSkip: 1 collect: aBlock The extra layer of function call doesn't add much overhead. On the other hand #overlappingPairsRemainderCollect: does lots of extra copying through #allButFirst: so would not be so good for reuse by  #overlappingPairsCollect:

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