Four is magic: Difference between revisions
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Forty billion one is seventeen, seventeen is nine, nine is four, four is magic.</pre> |
Forty billion one is seventeen, seventeen is nine, nine is four, four is magic.</pre> |
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'''Comment''' |
'''Comment''' |
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The solution is well modularised: <code>st</code> stringifies a number <1000; <code>s</code> stringifies a number; <code>fim</code> generates the sequence and formats it. |
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We see |
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* the Converge iterator <code>\</code> |
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* recursion through self-reference <code>.z.s</code> |
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* composition <code>count s@</code> |
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* Each Prior iterator <code>prior</code> |
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In q the same syntax applies a function to an argument or a list to its indexes. A consequence is that, with the Converge iterator <code>\</code> the lengths alone form a finite-state machine which can generate the convergence. |
In q the same syntax applies a function to an argument or a list to its indexes. A consequence is that, with the Converge iterator <code>\</code> the lengths alone form a finite-state machine which can generate the convergence. |
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q)sl\[19] |
q)sl\[19] |
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19 8 5 4</lang> |
19 8 5 4</lang> |
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Finally, we demonstrate the convergence using a cache of a million stringified numbers, and their lengths as a finite-state machine. |
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* [https://code.kx.com/q/learn/pb/four-magic/ The Q Playbook: Four is magic – analysis] |
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<lang q>q)sl:count each ten6:s each til 1000000 / stringify first million numbers and lengths |
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q)ten6 789123 |
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"seven hundred eighty nine thousand one hundred twenty three" |
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q)sl 789123 |
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59 |
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q)sl\[789123] / converge |
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789123 59 10 3 5 4 |
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q)1 fim 789123; / compare result |
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Seven hundred eighty nine thousand one hundred twenty three is fifty nine, fifty nine is ten, ten is three, three is five, five is four, four is magic.</lang> |
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=={{header|Racket}}== |
=={{header|Racket}}== |
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