197 lines
7.9 KiB
HTML
197 lines
7.9 KiB
HTML
<!doctype html>
|
|
<html lang="en">
|
|
<head>
|
|
<meta charset="UTF-8" />
|
|
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
|
|
<meta name="viewport" content="width=device-width, initial-scale=1" />
|
|
<link rel="stylesheet" href="/styles/common.css" />
|
|
<link rel="stylesheet" href="/styles/post.css" />
|
|
<link rel="icon" type="image/webp" href="/public/logo.webp" />
|
|
<link href="/public/prism/prism.css" rel="stylesheet" />
|
|
<link href="/public/prism/prism-theme.css" rel="stylesheet" />
|
|
<script defer src="/public/prism/prism.js"></script>
|
|
<script
|
|
src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"
|
|
async
|
|
></script>
|
|
<title>Barrett Ruth</title>
|
|
</head>
|
|
<body class="graph-background">
|
|
<header>
|
|
<a
|
|
href="/"
|
|
style="text-decoration: none; color: inherit"
|
|
onclick="goHome(event)"
|
|
>
|
|
<div class="terminal-container">
|
|
<span class="terminal-prompt">barrett@ruth:~$ /algorithms</span>
|
|
<span class="terminal-cursor"></span>
|
|
</div>
|
|
</a>
|
|
</header>
|
|
<main class="main">
|
|
<div class="post-container">
|
|
<header class="post-header">
|
|
<h1 class="post-title">Competitive Programming Log</h1>
|
|
</header>
|
|
<article class="post-article">
|
|
<h2>the beginning—12/2/2025</h2>
|
|
<div>
|
|
<p>
|
|
This marks the (true) beginning of my competitive programming
|
|
journey. By "true" I mean intentional, focused, daily practice.
|
|
Driven by my admiration for competitive programmers, love of
|
|
challenge, and desire for a decent new-grad job, I'm excited to
|
|
start putting in the work.
|
|
</p>
|
|
<p>
|
|
This webpage will be an archive of everything related to this
|
|
process, including my practice strategies, setup, shortcomings,
|
|
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/profile/sigill" target="_blank"
|
|
>sigill</a
|
|
>) 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>
|
|
</div>
|
|
<h2>
|
|
<a href="https://codeforces.com/contest/1955" target="_blank"
|
|
>938 (div. 3)</a
|
|
>—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>—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>
|
|
</div>
|
|
</main>
|
|
<script src="/scripts/common.js"></script>
|
|
<script src="/scripts/post.js"></script>
|
|
</body>
|
|
</html>
|