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    <p>The problem with your algorithm is your determination of <code>loc_pi</code>. For example, consider the case where 1000 is the first <code>pi</code> chosen in <code>loc_pi=seq.index(pi)</code>. In that case, <code>loc_pi</code> will equal 2 since 1000 is at index 2 of the sequence, and the function will return 1000, which we know is absolutely not order statistic 2.</p> <p>Thus, we know we can't determine <code>loc_pi</code> based on the index of the randomly chosen <code>pi</code>. After all, that list is in an arbitrary order- its position means nothing. What you are actually trying to get for that <code>loc_pi</code> value is <em>the number of elements in that sublist that are below your chosen pi</em>. And thankfully, that is easy to get! Just change the line:</p> <pre><code> return lo,pi,hi,loc_pi </code></pre> <p>to</p> <pre><code> return lo,pi,hi,len(lo) + 1 </code></pre> <p>And you'll find it performs correctly and consistently!</p> <pre><code>dynamic-oit-vapornet-c-913:test dgrtwo$ python test21.py Sequence [54, -1, 1000, 565, 64, 2, 5] Statistic pi 565 Location 3 pi 5 Location 5 pi -1 Location 0 pi 2 Location 0 2 dynamic-oit-vapornet-c-913:test dgrtwo$ python test21.py Sequence [54, -1, 1000, 565, 64, 2, 5] Statistic pi -1 Location 1 pi 54 Location 0 pi 5 Location 2 pi 2 Location 0 2 </code></pre> <p>ETA: Please also note that your algorithm as written will <em>not</em> always work if there are ties in the input sequence. Try a few examples and you will see what I mean. There are simple ways to solve it that I am sure you can figure out.</p>
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    1. USDavid Robinson
    1. USDavid Robinson
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    1. COI havent been able to test your suggestion yet, but out of curiosity shouldnt we return len(lo)+1, instead of len(lo), to include the pivot element as well?
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    2. COQuite right; I was thinking of indexed by 1 for some reason. Fixed (though now it will give a different output, I don't have the chance to change that)
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      1. USDavid Robinson
    3. CO:I tried to run to run the code with your suggestion but I get a totally weird output for instance with the input ` test_rselect([54,-1,1000,565,64,2,5],2)` I get :`@ubuntu:~/py-scripts$ python Dselect.py Sequence [54, -1, 1000, 565, 64, 2, 5] Statistic pi 54 Location 0 pi -1 Location 1 -1 `.Which really doesnt serve the purpose. Could you help?
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