--- /dev/null
+<!DOCTYPE html>
+<html lang="en-us">
+<head>
+<meta charset="utf-8"/>
+<title>Day 21 - Advent of Code 2021</title>
+<!--[if lt IE 9]><script src="/static/html5.js"></script><![endif]-->
+<link href='//fonts.googleapis.com/css?family=Source+Code+Pro:300&subset=latin,latin-ext' rel='stylesheet' type='text/css'/>
+<link rel="stylesheet" type="text/css" href="/static/style.css?26"/>
+<link rel="stylesheet alternate" type="text/css" href="/static/highcontrast.css?0" title="High Contrast"/>
+<link rel="shortcut icon" href="/favicon.png"/>
+</head><!--
+
+
+
+
+Oh, hello! Funny seeing you here.
+
+I appreciate your enthusiasm, but you aren't going to find much down here.
+There certainly aren't clues to any of the puzzles. The best surprises don't
+even appear in the source until you unlock them for real.
+
+Please be careful with automated requests; I'm not a massive company, and I can
+only take so much traffic. Please be considerate so that everyone gets to play.
+
+If you're curious about how Advent of Code works, it's running on some custom
+Perl code. Other than a few integrations (auth, analytics, social media), I
+built the whole thing myself, including the design, animations, prose, and all
+of the puzzles.
+
+The puzzles are most of the work; preparing a new calendar and a new set of
+puzzles each year takes all of my free time for 4-5 months. A lot of effort
+went into building this thing - I hope you're enjoying playing it as much as I
+enjoyed making it for you!
+
+If you'd like to hang out, I'm @ericwastl on Twitter.
+
+- Eric Wastl
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+-->
+<body>
+<header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2021/about">[About]</a></li><li><a href="/2021/events">[Events]</a></li><li><a href="https://teespring.com/stores/advent-of-code" target="_blank">[Shop]</a></li><li><a href="/2021/settings">[Settings]</a></li><li><a href="/2021/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <a href="/2021/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">42*</span></div></div><div><h1 class="title-event"> <span class="title-event-wrap">{:year </span><a href="/2021">2021</a><span class="title-event-wrap">}</span></h1><nav><ul><li><a href="/2021">[Calendar]</a></li><li><a href="/2021/support">[AoC++]</a></li><li><a href="/2021/sponsors">[Sponsors]</a></li><li><a href="/2021/leaderboard">[Leaderboard]</a></li><li><a href="/2021/stats">[Stats]</a></li></ul></nav></div></header>
+
+<div id="sidebar">
+<div id="sponsor"><div class="quiet">Our <a href="/2021/sponsors">sponsors</a> help make Advent of Code possible:</div><div class="sponsor"><a href="https://retool.com/?utm_source=sponsor&utm_medium=event&utm_campaign=adventofcode" target="_blank" onclick="if(ga)ga('send','event','sponsor','sidebar',this.href);" rel="noopener">Retool</a> - Build internal apps remarkably fast. Drag and drop a form together, and have it POST back to your API in minutes. Write JavaScript anywhere to customize. Deploy instantly with access controls and audit logs.</div></div>
+</div><!--/sidebar-->
+
+<main>
+<script>window.addEventListener('click', function(e,s,r){if(e.target.nodeName==='CODE'&&e.detail===3){s=window.getSelection();s.removeAllRanges();r=document.createRange();r.selectNodeContents(e.target);s.addRange(r);}});</script>
+<article class="day-desc"><h2>--- Day 21: Dirac Dice ---</h2><p>There's not much to do as you slowly descend to the bottom of the ocean. The submarine computer <span title="A STRANGE GAME.">challenges you to a nice game</span> of <em>Dirac Dice</em>.</p>
+<p>This game consists of a single <a href="https://en.wikipedia.org/wiki/Dice" target="_blank">die</a>, two <a href="https://en.wikipedia.org/wiki/Glossary_of_board_games#piece" target="_blank">pawns</a>, and a game board with a circular track containing ten spaces marked <code>1</code> through <code>10</code> clockwise. Each player's <em>starting space</em> is chosen randomly (your puzzle input). Player 1 goes first.</p>
+<p>Players take turns moving. On each player's turn, the player rolls the die <em>three times</em> and adds up the results. Then, the player moves their pawn that many times <em>forward</em> around the track (that is, moving clockwise on spaces in order of increasing value, wrapping back around to <code>1</code> after <code>10</code>). So, if a player is on space <code>7</code> and they roll <code>2</code>, <code>2</code>, and <code>1</code>, they would move forward 5 times, to spaces <code>8</code>, <code>9</code>, <code>10</code>, <code>1</code>, and finally stopping on <code>2</code>.</p>
+<p>After each player moves, they increase their <em>score</em> by the value of the space their pawn stopped on. Players' scores start at <code>0</code>. So, if the first player starts on space <code>7</code> and rolls a total of <code>5</code>, they would stop on space <code>2</code> and add <code>2</code> to their score (for a total score of <code>2</code>). The game immediately ends as a win for any player whose score reaches <em>at least <code>1000</code></em>.</p>
+<p>Since the first game is a practice game, the submarine opens a compartment labeled <em>deterministic dice</em> and a 100-sided die falls out. This die always rolls <code>1</code> first, then <code>2</code>, then <code>3</code>, and so on up to <code>100</code>, after which it starts over at <code>1</code> again. Play using this die.</p>
+<p>For example, given these starting positions:</p>
+<pre><code>Player 1 starting position: 4
+Player 2 starting position: 8
+</code></pre>
+<p>This is how the game would go:</p>
+<ul>
+<li>Player 1 rolls <code>1</code>+<code>2</code>+<code>3</code> and moves to space <code>10</code> for a total score of <code>10</code>.</li>
+<li>Player 2 rolls <code>4</code>+<code>5</code>+<code>6</code> and moves to space <code>3</code> for a total score of <code>3</code>.</li>
+<li>Player 1 rolls <code>7</code>+<code>8</code>+<code>9</code> and moves to space <code>4</code> for a total score of <code>14</code>.</li>
+<li>Player 2 rolls <code>10</code>+<code>11</code>+<code>12</code> and moves to space <code>6</code> for a total score of <code>9</code>.</li>
+<li>Player 1 rolls <code>13</code>+<code>14</code>+<code>15</code> and moves to space <code>6</code> for a total score of <code>20</code>.</li>
+<li>Player 2 rolls <code>16</code>+<code>17</code>+<code>18</code> and moves to space <code>7</code> for a total score of <code>16</code>.</li>
+<li>Player 1 rolls <code>19</code>+<code>20</code>+<code>21</code> and moves to space <code>6</code> for a total score of <code>26</code>.</li>
+<li>Player 2 rolls <code>22</code>+<code>23</code>+<code>24</code> and moves to space <code>6</code> for a total score of <code>22</code>.</li>
+</ul>
+<p>...after many turns...</p>
+<ul>
+<li>Player 2 rolls <code>82</code>+<code>83</code>+<code>84</code> and moves to space <code>6</code> for a total score of <code>742</code>.</li>
+<li>Player 1 rolls <code>85</code>+<code>86</code>+<code>87</code> and moves to space <code>4</code> for a total score of <code>990</code>.</li>
+<li>Player 2 rolls <code>88</code>+<code>89</code>+<code>90</code> and moves to space <code>3</code> for a total score of <code>745</code>.</li>
+<li>Player 1 rolls <code>91</code>+<code>92</code>+<code>93</code> and moves to space <code>10</code> for a final score, <code>1000</code>.</li>
+</ul>
+<p>Since player 1 has at least <code>1000</code> points, player 1 wins and the game ends. At this point, the losing player had <code>745</code> points and the die had been rolled a total of <code>993</code> times; <code>745 * 993 = <em>739785</em></code>.</p>
+<p>Play a practice game using the deterministic 100-sided die. The moment either player wins, <em>what do you get if you multiply the score of the losing player by the number of times the die was rolled during the game?</em></p>
+</article>
+<p>Your puzzle answer was <code>734820</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>Now that you're warmed up, it's time to play the real game.</p>
+<p>A second compartment opens, this time labeled <em>Dirac dice</em>. Out of it falls a single three-sided die.</p>
+<p>As you experiment with the die, you feel a little strange. An informational brochure in the compartment explains that this is a <em>quantum die</em>: when you roll it, the universe <em>splits into multiple copies</em>, one copy for each possible outcome of the die. In this case, rolling the die always splits the universe into <em>three copies</em>: one where the outcome of the roll was <code>1</code>, one where it was <code>2</code>, and one where it was <code>3</code>.</p>
+<p>The game is played the same as before, although to prevent things from getting too far out of hand, the game now ends when either player's score reaches at least <code><em>21</em></code>.</p>
+<p>Using the same starting positions as in the example above, player 1 wins in <code><em>444356092776315</em></code> universes, while player 2 merely wins in <code>341960390180808</code> universes.</p>
+<p>Using your given starting positions, determine every possible outcome. <em>Find the player that wins in more universes; in how many universes does that player win?</em></p>
+</article>
+<p>Your puzzle answer was <code>193170338541590</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
+<p>At this point, you should <a href="/2021">return to your Advent calendar</a> and try another puzzle.</p>
+<p>If you still want to see it, you can <a href="21/input" target="_blank">get your puzzle input</a>.</p>
+<p>You can also <span class="share">[Share<span class="share-content">on
+ <a href="https://twitter.com/intent/tweet?text=I%27ve+completed+%22Dirac+Dice%22+%2D+Day+21+%2D+Advent+of+Code+2021&url=https%3A%2F%2Fadventofcode%2Ecom%2F2021%2Fday%2F21&related=ericwastl&hashtags=AdventOfCode" target="_blank">Twitter</a>
+ <a href="javascript:void(0);" onclick="var mastodon_instance=prompt('Mastodon Instance / Server Name?'); if(typeof mastodon_instance==='string' && mastodon_instance.length){this.href='https://'+mastodon_instance+'/share?text=I%27ve+completed+%22Dirac+Dice%22+%2D+Day+21+%2D+Advent+of+Code+2021+%23AdventOfCode+https%3A%2F%2Fadventofcode%2Ecom%2F2021%2Fday%2F21'}else{return false;}" target="_blank">Mastodon</a
+></span>]</span> this puzzle.</p>
+</main>
+
+<!-- ga -->
+<script>
+(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
+ga('create', 'UA-69522494-1', 'auto');
+ga('set', 'anonymizeIp', true);
+ga('send', 'pageview');
+</script>
+<!-- /ga -->
+</body>
+</html>
\ No newline at end of file
projects / advent-of-code-21.git / commitdiff