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<h1 class="post-title">Competitive Programming Log</h1>
</header>
<article class="post-article">
<h2>
<a href="https://codeforces.com/contest/1857/" target="_blank"
>891 (div. 3)</a
>&mdash;{6,7}/5/2025
</h2>
<div>
<p>
Solved partially on the plane and at home. Best round in terms of
acceptance rate. After bombing another codeforces contest & more
CSES work, it's clear that my biggest weakness is
<b>algorithmic correctness and certainty</b>. To remedy:
</p>
<ul>
<li>Test edge cases (boundary + tricky)</li>
<li>Don't submit unless you're <i>certain</i> you're right</li>
<li>In analysis, leave no stone unturned (be thorough)</li>
<li>
Don't rely on the given test cases as proof of correctness.
</li>
</ul>
<ol>
<li>
A: ironically, although I got AC in ~1 minute, this is exactly
where I go wrong. I did not check the actual correctness of my
parity checks but submitted anyway.
</li>
<li>
B: AC once again but <b>implementation is still a weakness</b>.
In this case, it was due to a lack of problem understanding,
i.e. rounding up sets all right digits to 0, but carries can
still affect the number after that.
</li>
<li>
C: skipped and came back later. The idea of sorting came up but
I was overwhelmed. My end solution was a bit overcomplicated but
still logically sound. I'm getting better at making
observations, in this case explicitly identifying the fact that
the largest element must have one more element greater than or
equal to itself, permitting you to build the answer in reverse
order. <b>Did not prove the correctness of this</b>.
</li>
<li>
D: skipped and came back later. Given the large amount of
vertices I did a good job of rephrasing the data (thanks
<a
href="https://www.google.com/search?q=how+to+solve+it"
target="_blank"
>George Pólya</a
>) and <b>proving</b> the correctness with
transitivity/contradiction. Initial solution
complex&mdash;ponder implementation before going at it.
</li>
<li>
E: took me a while (I believe) because I was on a plane without
a notebook and visualizing was hard. Good mathematical
formulation, but initially returned the answer in wrong order.
<b
>Relied on the test cases to save me&mdash;ensure you're
solving the actual problem</b
>
(in this case, returning the queries in the right order).
</li>
<li>
F: Quadratic equation flew over my head. I was unsure but
should've just played with the numbers&mdash;if you plug them
in, you derive the quadratic equation relevant to the problem. I
then (maybe) could've gotten an answer. Instead, I was
intimidated because I thought I needed some fancy
DSA/dp/two-pointers/two-sum thing. Just have to build more
intuition. Also, totally did not know how to count number of
distinct pairs \(i, j\) with \(i\lt j\) for two elements. I
missed the case when the elements are equal and, yes, seriously
forgot it is just the product (I do not want to talk about it
but thanks Deepseek).
<b>Overflow, again. rly dude?</b>
</li>
<li>F: doing this later, got the core insight of the minimal weight edge path. Once again, for surveying path </li>
</ol>
</div>
<h2>cses (range queries, sorting and searching)&mdash;1/3/2025</h2>
<div>
<p>