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MathGroup Archive 2005

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Re: A list of numbers without "73"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63012] Re: [mg63005] A list of numbers without "73"
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 11 Dec 2005 04:56:34 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

Clear[S,S2];

S[1]=Range[1, 9];
S[i_?Positive]:=S[i]=
      Delete[Union[Table[
            k*(1-Boole[StringMatchQ[ToString[k], "*73*"]]),
            {k, 10^(i-1), 10^i-1}]], 1];

S2[1]=Range[1, 9];
S2[i_?Positive]:=S2[i]=
    DeleteCases[Range[10^(i-1), 10^i-1],
      _?(StringMatchQ[ToString[#], "*73*"]&)]

And@@Table[S[i]==S2[i],{i, 4}]

True

Timing[S[6]][[1]]

36.1983 Second

Timing[S2[6]][[1]]

28.961 Second

%/%%

0.800065

S[6]==S2[6]

True


Bob Hanlon

> 
> From: "Thomas Schmelzer" <thomas.??? at balliol.ox.ac.uk>
To: mathgroup at smc.vnet.net
> Date: 2005/12/10 Sat AM 06:03:40 EST
> Subject: [mg63012] [mg63005] A list of numbers without "73"
> 
> Experts,
> 
> S(i) should be a list of positive integers without the substring "73".
> 
> My code seems to be very inefficient. I multiply all numbers with 0 if they 
> contain "73", sort the new list, make the union (remove double elements) 
and 
> delete the first element. Therefore it is necessary to use an if statement 
> in order not to delete the first element of the numbers 1-9. Any more 
> sophisticated ideas?
> 
> L := Table[k, {k, 1, 9}]
> 
> S[i_] := S[i] =
> If[i == 1, L,
> Delete[Union[
> Table[k*(1 - Boole[StringMatchQ[ToString[k], "*73*"]]), {k,
> 10^(i - 1), 10^i - 1}]], 1]]
> 
> 
> 
> Best
> 
> Thomas
> 
> 
> 
> 
> 


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