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POVery large execution time differences for virtually same C++ and Python code
 

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  1. POVery large execution time differences for virtually same C++ and Python code
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    <p>I was trying to write a solution for <a href="http://projecteuler.net/problem=12" rel="nofollow">Problem 12 (Project Euler)</a> in Python. The solution was just too slow, so I tried checking up other people's solution on the internet. I found <a href="http://www.staticallylinked.com/2010/03/finding-first-triangle-number-to-have.html" rel="nofollow">this code</a> written in C++ which does virtually the same exact thing as my python code, with just a few insignificant differences.</p> <p>Python:</p> <pre><code>def find_number_of_divisiors(n): if n == 1: return 1 div = 2 # 1 and the number itself for i in range(2, n/2 + 1): if (n % i) == 0: div += 1 return div def tri_nums(): n = 1 t = 1 while 1: yield t n += 1 t += n t = tri_nums() m = 0 for n in t: d = find_number_of_divisiors(n) if m &lt; d: print n, ' has ', d, ' divisors.' m = d if m == 320: exit(0) </code></pre> <p>C++:</p> <pre><code>#include &lt;iostream&gt; int main(int argc, char *argv[]) { unsigned int iteration = 1; unsigned int triangle_number = 0; unsigned int divisor_count = 0; unsigned int current_max_divisor_count = 0; while (true) { triangle_number += iteration; divisor_count = 0; for (int x = 2; x &lt;= triangle_number / 2; x ++) { if (triangle_number % x == 0) { divisor_count++; } } if (divisor_count &gt; current_max_divisor_count) { current_max_divisor_count = divisor_count; std::cout &lt;&lt; triangle_number &lt;&lt; " has " &lt;&lt; divisor_count &lt;&lt; " divisors." &lt;&lt; std::endl; } if (divisor_count == 318) { exit(0); } iteration++; } return 0; } </code></pre> <p>The python code takes 1 minute and 25.83 seconds on my machine to execute. While the C++ code takes around 4.628 seconds. Its like 18x faster. I had expected the C++ code to be faster but not by this great margin and that too just for a simple solution which consists of just 2 loops and a bunch of increments and mods.</p> <p>Although I would appreciate answers on how to solve this problem, the main question I want to ask is <strong>Why is C++ code so much faster? Am I using/doing something wrongly in python?</strong></p> <hr> <p><strong>Replacing range with xrange:</strong></p> <p>After replacing range with xrange the python code takes around 1 minute 11.48 seconds to execute. (Around 1.2x faster)</p>
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    1. USAneesh Dogra
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      1. POVery large execution time differences for virtually same C++ and Python code
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    1. COConsider using `xrange` instead of `range`. Also just consider using C++
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    2. COIt's really late so my mind may be a little fuzzy, but one slight improvement to find the number of divisors would be to go only to sqrt(n) in your for loop instead of n/2+1 ... But you'd have to add 2 to div each time then. One for the divisor less than sqrt(n) and one for its codivisor(is that a word??)
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      1. USGeorge Mitchell
    3. COYeah, but he does that in both versions.
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      1. USJared
 

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