way to calculate 2**1000 without expanding it?

[zombie]

Hi guys,
i am writing a program to sum up the digits of a number 2**1000?
Is there a way/formula to do it without expanding it?

 

[Arnaud Delobelle]

Hi guys,
        i am writing a program to sum up the digits of a number 2**1000?
Is there a way/formula to do it without expanding it?

In base 2, the answer is 1

Hopefully-helpfully-but-not-so-sure'ly yours,

 

[Ian Kelly]

Hi guys,
        i am writing a program to sum up the digits of a number 2**1000?
Is there a way/formula to do it without expanding it?

Possibly, but why worry about it? It's only around 300 digits.

Since this sounds like homework, I won't post the one-liner I used to
do it the brute-force way, but I will note that it takes about 200
microseconds to run on my laptop.

Cheers,
Ian

 

[Prasad, Ramit]

Hi guys,

Since this sounds like homework, I won't post the one-liner I used to
do it the brute-force way, but I will note that it takes about 200
microseconds to run on my laptop.

If you happen to be new to Python, I will say I used these functions to create a one liner (in alphabetical order).

Int
Lambda
Map
Reduce
Str


Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423


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[Arnaud Delobelle]

Possibly, but why worry about it?  It's only around 300 digits.

Since this sounds like homework, I won't post the one-liner I used to
do it the brute-force way, but I will note that it takes about 200
microseconds to run on my laptop.

Ah go on, let's make a codegolf contest out of it.
My entry:
1366

 

[Ian Kelly]

Ah go on, let's make a codegolf contest out of it.
My entry:

1366

That is exactly what mine was.

 

[Gary Herron]

Ah go on, let's make a codegolf contest out of it.
My entry:

1366

Here's another one-liner using a generator instead of map:

sum(int(c) for c in str(2**1000))

Gary Herron

 

[Stefan Krah]

Here's another one-liner using a generator instead of map:

sum(int(c) for c in str(2**1000))

The OP did not specify the base:
1


Or just:
1


Stefan Krah

 

[Prasad, Ramit]

sum(map(int,str(2**1000)))
*smacks face* Gah, forgot about sum.

Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423



This email is confidential and subject to important disclaimers and
conditions including on offers for the purchase or sale of
securities, accuracy and completeness of information, viruses,
confidentiality, legal privilege, and legal entity disclaimers,
available at http://www.jpmorgan.com/pages/disclosures/email.

 

[Steven D'Aprano]

Ah go on, let's make a codegolf contest out of it.
My entry:

1366

Time for some obfuscated Python!

b = (16,13624)
for i in range(23, 42, 3):
b = (b[0]*b[0], b[1]+1024)

for j in range(12345, 8929, -7):
b = (b[0]+b[0], b[1]-3)

while b > (0,9876):
b = tuple((lambda a,b: map(lambda a,b:a+b, a,b))
((lambda a,b: map(lambda a,b:a*b, a,b))
(b,(0,1)), (lambda a,b: map(lambda a,b:a-b, a,b))
(divmod(b[0],10),(0,64))))

print b[1]

 

[Grant Edwards]

Here's another one-liner using a generator instead of map:

sum(int(c) for c in str(2**1000))

Just in case you can't spare the 3KB required for the list of integers
that map creates.

In this case it doesn't matter, but it's not hard to find problems
where the difference between the memory requirements for a generator
and a map/list-comprehension are significant enough to worry about.

 

[Ian Kelly]

Just in case you can't spare the 3KB required for the list of integers
that map creates.

In this case it doesn't matter, but it's not hard to find problems
where the difference between the memory requirements for a generator
and a map/list-comprehension are significant enough to worry about.

Unless otherwise specified, I generally assume that code on this list
is for Python 3, and map in Python 3 returns an iterator.

Cheers,
Ian

 

[Grant Edwards]

Unless otherwise specified, I generally assume that code on this list
is for Python 3, and map in Python 3 returns an iterator.

Indeed, I forgot about that (I'm still using Python 2 since I use some
libraries that haven't been ported).

 

[Mark Dickinson]

Ah go on, let's make a codegolf contest out of it.
My entry:

You could save another character by replacing "2**1000" with "2<<999"