Question

I started learning programming a few months ago and just recently found codechef.
The problem is that on problems that use large amounts of input my code alwaqys exceehe time limit. I can’t even seem to make the input test work.

Description from codechef:

Input

The input begins with two positive integers n k (n, k<=10^7). The next
n lines of input contain one positive integer ti, not greater than
10^9, each.

Output

Write a single integer to output, denoting how many integers ti are
divisible by k.

Here’s the code:

n, t = [int(x) for x in input().split()]
c = 0
for i in range(n):
    if not int(input()) % t:
        c += 1
print(c)

I’m not sure what I’m missing. How can I handle this faster?

Answer 1

This should really be a comment, but anyway.

Note that there’s an accepted Python 2 solution here, with runtime 45.77s, so it’s clearly possible. I think you’re a victim of Python 3’s slow I/O (looks like they’re using 3.1.2). On a two million line input file (which happens not to have any numbers which are divisible): there’s not much difference when there are a lot), on a version of your code modified to be compatible with 2 and 3, I get:

~/coding$ time python2.6 enormread.py < sample.txt 
0

real    0m3.971s
user    0m3.712s
sys 0m0.256s
~/coding$ time python2.7 enormread.py < sample.txt 
0

real    0m2.637s
user    0m2.428s
sys 0m0.204s
~/coding$ time python3.2 enormread.py < sample.txt 
0

real    0m10.412s
user    0m10.065s
sys 0m0.344s
~/coding$ time ~/sys/Python-3.3.0a2/python enormread.py < sample.txt 
0

real    0m6.776s
user    0m6.336s
sys 0m0.436s
~/coding$ time pypy enormread.py < sample.txt 
0

real    0m2.211s
user    0m1.948s
sys 0m0.028s

To throw @agf’s (sum(not int(line) % t for line in sys.stdin[.buffer])) into the mix:

~/coding$ time python2.7 enormfast.py < sample.txt 
0

real    0m1.454s
user    0m1.436s
sys 0m0.016s
~/coding$ time python3.2 enormfast.py < sample.txt 
0

real    0m2.243s
user    0m2.228s
sys 0m0.012s