In coding competitions we encounter inputs like:
2 3
4 5
So we do the following:
m, n = [int(x) for x in raw_input().split(' ')]
Is there a faster way of doing the same thing?
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3What do you mean by "faster"? Execution time or less code?phant0m– phant0m2012-10-08 15:06:53 +00:00Commented Oct 8, 2012 at 15:06
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2 Answers
For all practical purposes, That's about as fast as you can get. On some machines, you may see a speedup on the order or a couple percent if you go with map instead of a list comprehension, but that's not guaranteed.
Here's some quick timings on my machine:
from itertools import imap
#map
>>> timeit.timeit('x,y = map(int,line.split(" "))','from __main__ import line')
4.7857139110565186
>>> timeit.timeit('x,y = map(int,line.split())','from __main__ import line')
4.5680718421936035
#list comprehension
>>> timeit.timeit('x,y = [int(x) for x in line.split(" ")]','from __main__ import line')
4.3816750049591064
>>> timeit.timeit('x,y = [int(x) for x in line.split()]','from __main__ import line')
4.3246541023254395
#itertools.imap
>>> timeit.timeit('x,y = imap(int,line.split(" "))','from __main__ import line,imap')
4.431504011154175
>>> timeit.timeit('x,y = imap(int,line.split())','from __main__ import line,imap')
4.3257410526275635
#generator expression
>>> timeit.timeit('x,y = (int(x) for x in line.split(" "))','from __main__ import line')
4.897794961929321
>>> timeit.timeit('x,y = (int(x) for x in line.split())','from __main__ import line')
4.732620000839233
Surprisingly, split() seems to perform better than split(" ").
If you're guaranteed to have ascii input of numbers between 0 and 9, you can do a good bit better using ord:
>>>timeit.timeit('x,y = [ord(x)-48 for x in line.split(" ")]','from __main__ import line')
1.377655029296875
>>> timeit.timeit('x,y = [ord(x)-48 for x in line.split()]','from __main__ import line')
1.3243558406829834
But that imposes a severe restriction on your inputs.
One other idea that you could try (I have no idea what the performance implications would be), but you could read your lines from sys.stdin:
import sys
for line in sys.stdin:
x,y = [ord(x)-48 for x in line.split()]
3 Comments
Jon Clements
split() and split(" ") don't actually do the same thing... docs.python.org/library/stdtypes.html#str.split
mgilson
@JonClements -- I understand that they're not the same.
split() and split(None) are the same. However, split() is more general than split(" ") which is why I'm surprised that it is faster (it needs to do test for "\t" instead of just ' ', or runs of ' ' instead of single ' ' for example)Jon Clements
I'm guessing then that
split() is probably using something like strtok(str, " \t") in C which deals with consecutive delimiters... While, split(' ') has to go against that behaviour (and also potentially build a larger result list with ''s)Use map(), it's faster than list comprehensions when used with built-in functions:
m, n = map(int, raw_input().split())
answered Oct 8, 2012 at 14:55
Ashwini Chaudhary
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3 Comments
Ashwini Chaudhary
mgilson
Yes, I'm aware of this. I've done the timings myself many times (and gotten conflicting results). All I'm saying is that the results can vary from machine to machine and that this sort of micro-optimization is unlikely to make any real difference.
pyronic
on using map in my submission,execution time reduced from 3.86 to 3.64 seconds