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</header> </header>
<article class="post-article"> <article class="post-article">
<h2>the beginning&mdash;12/2/2025</h2> <h2>the beginning&mdash;12/2/2025</h2>
<div>
<p> <p>
This marks the (true) beginning of my competitive programming This marks the (true) beginning of my competitive programming
journey. By "true" I mean intentional, focused, daily practice. journey. By "true" I mean intentional, focused, daily practice.
@ -45,14 +46,148 @@
</p> </p>
<p> <p>
This webpage will be an archive of everything related to this This webpage will be an archive of everything related to this
process, including my practice strategies, setup, shortcomings, logs, and process, including my practice strategies, setup, shortcomings,
more. For now, I'll be practicing on logs, and more. For now, I'll be practicing on
<a href="https://codeforces.com" target="_blank">CodeForces</a> (account <a href="https://codeforces.com" target="_blank">CodeForces</a>
<a href="https://codeforces.com/profile/sigill" target="_blank">sigill</a>) and (account
<a href="https://cses.fi" target="_blank">CSES</a>, using the <a href="https://codeforces.com/profile/sigill" target="_blank"
<a href="https://cses.fi/book/book.pdf" target="_blank">CP Handbook</a> and browsing by related problem tags with >sigill</a
ever-increasing difficulty. >) and <a href="https://cses.fi" target="_blank">CSES</a>, using
the
<a href="https://cses.fi/book/book.pdf" target="_blank"
>CP Handbook</a
>
and browsing by related problem tags with ever-increasing
difficulty.
</p> </p>
</div>
<h2>
<a href="https://codeforces.com/contest/1955" target="_blank"
>938 (div. 3)</a
>&mdash;15/2/2025
</h2>
<div class="fold">
<p>
What would've been my best contest. Unfortunately, CodeForces
decided to go down for TREE[3] centuries, which absolutely ruined
my groove in the contest and terminated my virtual. No excuses,
though, as I set a timer and finished up later.
</p>
</div>
<h3>A</h3>
<p>Brute-forced it but it still took me a few minutes.</p>
<ul>
<li>Read (and exploit) problem constraints</li>
<li>
Go back and derive the linear optimization (choosing the one with
better marginal utility)
</li>
<li>If you have a (simple enough) solution, just go with it.</li>
</ul>
<h3>B</h3>
<p>
Easily recognized how to form the matrix (i.e. smallest element
first with positive integers \(c,d\)) but tripped up on the
implementation.
</p>
<ul>
<li>
Flesh out the steps before coding (i.e. walk through iterations in
head, transitions, edge cases on the rows and columns, i.e.
checking if <code>i==n-1</code>) <i>especially</i> on
implementation-heavy problems
</li>
</ul>
<h3>C</h3>
<p>
Did a horrific (but correct) binary search solution. Tripped up by
specifics of <code>std::{upper,lower}_bound</code> regardless.
Technically, generating the prefix and postfix arrays takes two
passes and two binary searches to find the answer but this is still
more inefficient than the trivial linear scan.
</p>
<ul>
<li>THE INT OVERFLOW INCIDENT</li>
<li>
Deepen understanding of binary search & STL functions to the point
that it is second nature
</li>
<li>Consider simple solutions first.</li>
</ul>
<h3>D</h3>
<p>
Instantly recognized sliding window but struggled with minor details
(i.e. keeping track of match count) by rushing to the solution.
</p>
<ul>
<li>
Problem statement took a long time to grasp. Look at examples and
just read through slower (don't rush!)
</li>
<li>
Sliding window grasp isn't <i>rigorous</i>&mdash;improve this
later
</li>
<li>
When you don't remember 100% of how an algorithm works,
<b>mentally walk through a few iterations</b>
</li>
<li>Improve PBDS API familiarity (practice)</li>
</ul>
<h3>E</h3>
<p>
I had mentally tapped out by this point (I submitted a TLE \(O(n^2k)
solution without using my brain\). I solved F first, then took a
look at G <i>before</i> coming back to E, robbing me of 10 minutes
that could've been the difference between another solve.
</p>
<ul>
<li>
You're not like that. Solve problems in order (most of the time,
although skipping to F first was a wise decision).
</li>
<li>
Consider ideas <i>fully</i> before dropping them. I considered the
difference array, then <i>discarded</i> it, erroneously believing
a boolean was sufficient and completely forgetting that the
concept of ranges complicates flipping.
</li>
<li>
Formalize constraints more clearly to help form a solution. For
example, the idea that flipping things twice makes no difference,
permitting the use of a boolean difference array.
</li>
<li>
Prove correctness. I didn't prove that iterating left to right,
toggling a range of k actually would always give a correct answer.
</li>
</ul>
<h3>F</h3>
<p>
Had the solution quickly but overcomplicated the implementation.
Walked through the examples and took my time.
</p>
<ul>
<li>
Failed to formalize the answer to the problem. I noticed patterns
but should've strictly defined the following rule: "Every even
count of a number contributes one to the score. Further, one
triple of 1, 2, 3 also contributes one." Ultimately, I ended up
submitting something I wasn't certain would be correct.
</li>
</ul>
<h3>G</h3>
<p>
Wasted time believing this was primitive DP, when it totally wasn't.
</p>
<ul>
<li>You're not that guy (yet >:))</li>
<li>
Prove optimal substructure and overlapping subproblems before
using DP & walk through the test cases. In this case, test case 3
immediately disproves dp.
</li>
</ul>
</article> </article>
</div> </div>
</main> </main>