Hello CodeForces Community,
Input / Output in Python can be sometimes time taking in cases when the input is huge or we have to output many number of lines, or a huge number of arrays(lists) line after line.
I have come across many questions on CodeForces where the style of taking input and printing makes your code quite faster.
For Input :-
Normally, the input is taken from STDIN in the form of String using
input(). And this STDIN is provided in the Judge's file. So why not try reading the input directly from the Judge's file using the Operating system(os) module, and input / output(io) module. This reading can be done in the form of bytes.
The code for that would be :-
import io,os input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline
or a native method (which can be used for not too large inputs) :-
import sys input = sys.stdin.readline
Now for Output :-
Instead of throwing the output to the STDOUT, we can try writing to the Judge's sytem file. The code for that would be to use
sys.stdout.write instead of
For printing an integer, instead of
sys.stdout.write(str(n) + "\n")
For printing a list of integers, instead of
sys.stdout.write(" ".join(map(str,list)) + "\n")
Now Program examples On CodeForces, where this was useful :-
I want to add something. When using BytesIO method of input, reading strings does not work normally like the STDIN method. Rather it returns a bytecoded string (I say bytecoded string, I am not sure what it's really called).
Suppose you input a string
somestringas follows, and then print it
It will print
somestring. If you want to print
somestringyou will have to decode the bytecoded string, and do something like this:
So, the overall code will be:
Remember this only happens in the case of strings. Integers behave normally.
Thanks a lot! I was getting TLE of 2 sec problem. After implementing this i made it in 1091 ms. It is very very helpful when you have to take input or give output in a loop/several times.
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readlineand it just returns empty string without waiting for input.
What am I doing wrong?
whole code please?
Using it in shell for example:
Looks like this code needs to read input from I/O redirection. Use it like:
$ python3 test.py < input.txt
And, do you know why 147370723 didn't work? The previous submission (147342596) got TL, and I just used this method of input for list "a" in the next one.
I just modified your solution and tested a bit, it can be TLE again (no runtime error) but still not passing the tests.
You can refer to 147473106 which is what I got after modifying your implementation. I use
listto indicate whether a row/col is colored or not.
I took a look at your solution and updated mine (147482726); yours got AC and mine TL again. (I wonder why)
But finally I could use this method of input. As it seems, it should not be mixed with other methods.
And the big question for me is that why
io.BytesIO(os.read(0, os.fstat(0).st_size)).readlinecant be used in place of the
inputvariable it is assigned to. (it would return empty string)
i am getting an error while using this line of code:
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline
Which language is the best for competitive programming.
Well, each language has strength and weakness.
Python is very convenient, but the speed is very slow and you will easily get TLE. C++ is mainstream language and very fast, but it is easy to fail system test, like forget long long int and some variable numbers may exceed 2147483647.
Java, go, swift also have pro and cons.
The best strategy is that you should master more than one language, one fast and one slow, like c++ and python. For loose constraint problem, use python to save time, and for tight constraint problem, use C++ to get passed.
Hey! I have used above methods but they do not work for me , even if they are working on my local machine .Please check these submissions 164067953 and 164066429 and help me to recitify the mistakes. Thank you
The solutions have Wrong Answer because your logic is incorrect....
Fast Input / Output will only work if your logic is correct (obviously) :p
Please check my 164064020 . It is only TLE. Can you look it in again?
This segment is causing TLE
Thank you so much. It's what I was needing.
Can confirm that changing the code from print to sys.stdout.write turned a TLE (https://codeforces.com/contest/1726/submission/208423821) to AC (https://codeforces.com/contest/1726/submission/208424281)
Note that changing the input to sys.stdin.readline didn't make a difference for this particular problem (ie getting AC using the plain built-in input function). This must be because this particular problem is write heavy (reads two numbers per test case, prints out up to 10**5 per testcase). I will just use sys.stdin and sys.stdout always in the future, to cover both read heavy and write heavy problems.