User:Yeti: Difference between revisions
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=DC/Questions/DROP= |
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TODO Drop top of stack without side effects |
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<pre> |
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# assume there is a value in x[1337], e.g. "gold" |
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[gold] 1337 :x |
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# "trash" on the stack: |
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[trash] |
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# push x[1337] to x-stack |
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1337;x Sx |
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# deposit TOS in x[1337] |
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1337: |
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# top of x-stack to x[1337] |
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Lx 1337: |
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1337 ;x |
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[Stack: ]PAP f |
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</pre> |
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{{out}} |
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<pre> |
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Stack: |
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gold |
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</pre> |
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Sigh! |
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Is there really no simpler way to drop the top of stack that works for strings and numbers and in all versions of Dc? |
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=Python/Primes/FSOE= |
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{{works with|Python|2.x}} |
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This is a sequentialised variant of the well known sieve method (ab)using a dictionary as sparse array. |
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Alternatively you can describe it as finding the wheels and moving them on a tape. The only knowledge is to start looking 2 instead of starting with 1, but the original sieve does skip 1 too. 2 is not hard coded to be prime. The algorithm detects it as 1st prime and then puts the 2-wheel on the tape. |
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A tape position can hold multiple wheels. |
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<lang python>L = {} |
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n = 2 |
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while 1: |
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if n in L: |
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P = L[n] |
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del L[n] # optional - saves some memory. |
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else: |
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print n |
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P = [n] |
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for p in P: |
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npp = n+p |
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if npp in L: |
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L[npp].add(p) |
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else: |
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L[npp] = set([p]) |
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n += 1</lang> |
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{{out}} |
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<pre> |
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29 |
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</pre> |
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...the program has to be terminated by the user e.g. by typing ctrl-c. |
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---- |
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{{mylangbegin}} |
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{{mylang|AWK|}} |
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{{mylang|C|}} |
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{{mylang|Dc|}} |
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{{mylang|Spin|}} |
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{{mylangend}} |