problems/day03.html

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  16 Oh, hello!  Funny seeing you here.
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  18 I appreciate your enthusiasm, but you aren't going to find much down here.
  19 There certainly aren't clues to any of the puzzles.  The best surprises don't
  20 even appear in the source until you unlock them for real.
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  22 Please be careful with automated requests; I'm not a massive company, and I can
  23 only take so much traffic.  Please be considerate so that everyone gets to play.
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  25 If you're curious about how Advent of Code works, it's running on some custom
  26 Perl code. Other than a few integrations (auth, analytics, ads, social media),
  27 I built the whole thing myself, including the design, animations, prose, and
  28 all of the puzzles.
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  30 The puzzles are most of the work; preparing a new calendar and a new set of
  31 puzzles each year takes all of my free time for 4-5 months. A lot of effort
  32 went into building this thing - I hope you're enjoying playing it as much as I
  33 enjoyed making it for you!
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  35 If you'd like to hang out, I'm @ericwastl on Twitter.
  36
  37 - Eric Wastl
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  90 <header><div><h1 class="title-global"><a href="/">Advent of Code</a></h1><nav><ul><li><a href="/2019/about">[About]</a></li><li><a href="/2019/events">[Events]</a></li><li><a href="https://teespring.com/adventofcode-2019" target="_blank">[Shop]</a></li><li><a href="/2019/settings">[Settings]</a></li><li><a href="/2019/auth/logout">[Log Out]</a></li></ul></nav><div class="user">Neil Smith <a href="/2019/support" class="supporter-badge" title="Advent of Code Supporter">(AoC++)</a> <span class="star-count">8*</span></div></div><div><h1 class="title-event">&nbsp;&nbsp;&nbsp;<span class="title-event-wrap">sub y{</span><a href="/2019">2019</a><span class="title-event-wrap">}</span></h1><nav><ul><li><a href="/2019">[Calendar]</a></li><li><a href="/2019/support">[AoC++]</a></li><li><a href="/2019/sponsors">[Sponsors]</a></li><li><a href="/2019/leaderboard">[Leaderboard]</a></li><li><a href="/2019/stats">[Stats]</a></li></ul></nav></div></header>
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  97 <article class="day-desc"><h2>--- Day 3: Crossed Wires ---</h2><p>The gravity assist was successful, and you're well on your way to the Venus refuelling station.  During the rush back on Earth, the fuel management system wasn't completely installed, so that's next on the priority list.</p>
  98 <p>Opening the front panel reveals a jumble of wires. Specifically, <em>two wires</em> are connected to a central port and extend outward on a grid.  You trace the path each wire takes as it leaves the central port, one wire per line of text (your puzzle input).</p>
  99 <p>The wires <span title="A jumble of twisty little wires, all alike.">twist and turn</span>, but the two wires occasionally cross paths. To fix the circuit, you need to <em>find the intersection point closest to the central port</em>. Because the wires are on a grid, use the <a href="https://en.wikipedia.org/wiki/Taxicab_geometry">Manhattan distance</a> for this measurement. While the wires do technically cross right at the central port where they both start, this point does not count, nor does a wire count as crossing with itself.</p>
 100 <p>For example, if the first wire's path is <code>R8,U5,L5,D3</code>, then starting from the central port (<code>o</code>), it goes right <code>8</code>, up <code>5</code>, left <code>5</code>, and finally down <code>3</code>:</p>
 101 <pre><code>...........
 102 ...........
 103 ...........
 104 ....+----+.
 105 ....|....|.
 106 ....|....|.
 107 ....|....|.
 108 .........|.
 109 .o-------+.
 110 ...........
 111 </code></pre>
 112 <p>Then, if the second wire's path is <code>U7,R6,D4,L4</code>, it goes up <code>7</code>, right <code>6</code>, down <code>4</code>, and left <code>4</code>:</p>
 113 <pre><code>...........
 114 .+-----+...
 115 .|.....|...
 116 .|..+--X-+.
 117 .|..|..|.|.
 118 .|.-<em>X</em>--+.|.
 119 .|..|....|.
 120 .|.......|.
 121 .o-------+.
 122 ...........
 123 </code></pre>
 124 <p>These wires cross at two locations (marked <code>X</code>), but the lower-left one is closer to the central port: its distance is <code>3 + 3 = 6</code>.</p>
 125 <p>Here are a few more examples:</p>
 126 <ul>
 127 <li><code>R75,D30,R83,U83,L12,D49,R71,U7,L72<br/>U62,R66,U55,R34,D71,R55,D58,R83</code> = distance <code>159</code></li>
 128 <li><code>R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51<br/>U98,R91,D20,R16,D67,R40,U7,R15,U6,R7</code> = distance <code>135</code></li>
 129 </ul>
 130 <p><em>What is the Manhattan distance</em> from the central port to the closest intersection?</p>
 131 </article>
 132 <p>Your puzzle answer was <code>1225</code>.</p><article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>It turns out that this circuit is very timing-sensitive; you actually need to <em>minimize the signal delay</em>.</p>
 133 <p>To do this, calculate the <em>number of steps</em> each wire takes to reach each intersection; choose the intersection where the <em>sum of both wires' steps</em> is lowest. If a wire visits a position on the grid multiple times, use the steps value from the <em>first</em> time it visits that position when calculating the total value of a specific intersection.</p>
 134 <p>The number of steps a wire takes is the total number of grid squares the wire has entered to get to that location, including the intersection being considered. Again consider the example from above:</p>
 135 <pre><code>...........
 136 .+-----+...
 137 .|.....|...
 138 .|..+--X-+.
 139 .|..|..|.|.
 140 .|.-X--+.|.
 141 .|..|....|.
 142 .|.......|.
 143 .o-------+.
 144 ...........
 145 </code></pre>
 146 <p>In the above example, the intersection closest to the central port is reached after <code>8+5+5+2 = <em>20</em></code> steps by the first wire and <code>7+6+4+3 = <em>20</em></code> steps by the second wire for a total of <code>20+20 = <em>40</em></code> steps.</p>
 147 <p>However, the top-right intersection is better: the first wire takes only <code>8+5+2 = <em>15</em></code> and the second wire takes only <code>7+6+2 = <em>15</em></code>, a total of <code>15+15 = <em>30</em></code> steps.</p>
 148 <p>Here are the best steps for the extra examples from above:</p>
 149 <ul>
 150 <li><code>R75,D30,R83,U83,L12,D49,R71,U7,L72<br/>U62,R66,U55,R34,D71,R55,D58,R83</code> = <code>610</code> steps</li>
 151 <li><code>R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51<br/>U98,R91,D20,R16,D67,R40,U7,R15,U6,R7</code> = <code>410</code> steps</li>
 152 </ul>
 153 <p><em>What is the fewest combined steps the wires must take to reach an intersection?</em></p>
 154 </article>
 155 <p>Your puzzle answer was <code>107036</code>.</p><p class="day-success">Both parts of this puzzle are complete! They provide two gold stars: **</p>
 156 <p>At this point, you should <a href="/2019">return to your Advent calendar</a> and try another puzzle.</p>
 157 <p>If you still want to see it, you can <a href="3/input" target="_blank">get your puzzle input</a>.</p>
 158 <p>You can also <span class="share">[Share<span class="share-content">on
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