Revisions to Happy 2K prime question

added 215 characters in body

edited Jul 1, 2012 at 15:10

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This answer should be read upside down, since the last edit has the fastest, neatest and shortest answer

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

EDIT2

Slightly faster but I like it twice as much

happyQ[1] = True; e : happyQ[i_] := (e = False; e = happyQ[#.# &@IntegerDigits[i]])

or perhaps to make it slightly shorter and a little bit more memory efficient, reducing the recursion tree's height

happyQ[1] = True; e : happyQ[i_] := e = happyQ[e = False; #.# &@IntegerDigits[i]]

This answer should be read upside down, since the last edit has the fastest, neatest and shortest answer

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

EDIT2

Slightly faster but I like it twice as much

happyQ[1] = True; e : happyQ[i_] := (e = False; e = happyQ[#.# &@IntegerDigits[i]])

This answer should be read upside down, since the last edit has the fastest, neatest and shortest answer

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

EDIT2

Slightly faster but I like it twice as much

happyQ[1] = True; e : happyQ[i_] := (e = False; e = happyQ[#.# &@IntegerDigits[i]])

or perhaps to make it slightly shorter and a little bit more memory efficient, reducing the recursion tree's height

happyQ[1] = True; e : happyQ[i_] := e = happyQ[e = False; #.# &@IntegerDigits[i]]

added 154 characters in body; added 108 characters in body

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edited Jun 29, 2012 at 18:29

Rojo

43.1k
7
100
196

This answer should be read upside down, since the last edit has the fastest, neatest and shortest answer

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

EDIT2

Slightly faster but I like it twice as much

happyQ[1] = True; e : happyQ[i_] := (e = False; e = happyQ[#.# &@IntegerDigits[i]])

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

This answer should be read upside down, since the last edit has the fastest, neatest and shortest answer

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

EDIT2

Slightly faster but I like it twice as much

happyQ[1] = True; e : happyQ[i_] := (e = False; e = happyQ[#.# &@IntegerDigits[i]])

deleted 2 characters in body

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edited Jun 21, 2012 at 15:03

Rojo

43.1k
7
100
196

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]^2]#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]^2])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

Module[{$guard = True}, happyQ[i_] /; $guard := Block[{$guard = False, appeared}, appeared[_] = False; happyQ[i] ] ] e : happyQ[_?appeared] := e = False; happyQ[1] = True; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.#&@IntegerDigits[i]])

Now, taking this from @LeonidShiffrin

happyPrimeN[n_] := Module[{m = 0, pctr = 0}, While[m < n, If[happyQ@Prime[++pctr], m++]]; {pctr, Prime[pctr]}];

EDIT

Ok, this was cool, but if you don't mind wasting a little memory and not resetting appeared, it becomes simple and less cool

appeared[_] = False; happyQ[1] = True; happyQ[_?appeared] = False; e : happyQ[i_] := e = (appeared[i] = True; happyQ[#.# &@IntegerDigits[i]])

deleted 1 characters in body

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edited Jun 21, 2012 at 11:03

Rojo

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Post Made Community Wiki by Mr.Wizard

occurred Jun 21, 2012 at 0:41

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edited Jun 21, 2012 at 0:29

Rojo

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edited Jun 21, 2012 at 0:00

Rojo

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answered Jun 20, 2012 at 23:48

Rojo

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