User:Yeti

From Rosetta Code

Dc/Questions/DROP[edit]

TODO Drop top of stack without side effects

# assume there is a value in x[1337], e.g. "gold"
[gold] 1337 :x

# "trash" on the stack:
[trash]

# push x[1337] to x-stack
1337;x Sx
# deposit TOS in x[1337]
1337:
# top of x-stack to x[1337]
Lx 1337:

1337 ;x

[Stack: ]PAP f
Output:
Stack: 
gold

Sigh!

Is there really no simpler way to drop the top of stack that works for strings and numbers and in all versions of Dc?

Python/Primes/FSOE[edit]

Works with: Python version 2.x

This is a sequentialised variant of the well known sieve method (ab)using a dictionary as sparse array.

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.

Python/Primes/FSOE1[edit]

Variant: A tape position can hold multiple wheels.

L = {}
n = 2
 
while 1:
 
if n in L:
P = L[n]
del L[n] # optional - saves some memory.
else:
print n
P = [n]
 
for p in P:
npp = n+p
if npp in L:
L[npp].add(p)
else:
L[npp] = set([p])
 
n += 1
Output:
2
3
5
7
11
13
17
19
23
29

...the program has to be terminated by the user e.g. by typing ctrl-c.

Python/Primes/FSOE3[edit]

Works with: Python version 2.x

Variant: A tape position can hold one wheel.

L = {}
n = 2
 
while 1:
 
if n in L:
P = L[n]
del L[n] # optional - saves some memory.
else:
P = n
print n
 
m = n+P
while m in L:
m += P
L[m] = P
 
n += 1
Output:
2
3
5
7
11
13
17
19
23
29

...the program has to be terminated by the user e.g. by typing ctrl-c.


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