Jake Pullen
79 lines
5.6 KiB
Markdown
79 lines
5.6 KiB
Markdown
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<article class="day-desc"><h2>--- Day 17: Clumsy Crucible ---</h2><p>The lava starts flowing rapidly once the Lava Production Facility is operational. As you <span title="see you soon?">leave</span>, the reindeer offers you a parachute, allowing you to quickly reach Gear Island.</p>
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<p>As you descend, your bird's-eye view of Gear Island reveals why you had trouble finding anyone on your way up: half of Gear Island is empty, but the half below you is a giant factory city!</p>
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<p>You land near the gradually-filling pool of lava at the base of your new <em>lavafall</em>. Lavaducts will eventually carry the lava throughout the city, but to make use of it immediately, Elves are loading it into large <a href="https://en.wikipedia.org/wiki/Crucible" target="_blank">crucibles</a> on wheels.</p>
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<p>The crucibles are top-heavy and pushed by hand. Unfortunately, the crucibles become very difficult to steer at high speeds, and so it can be hard to go in a straight line for very long.</p>
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<p>To get Desert Island the machine parts it needs as soon as possible, you'll need to find the best way to get the crucible <em>from the lava pool to the machine parts factory</em>. To do this, you need to minimize <em>heat loss</em> while choosing a route that doesn't require the crucible to go in a <em>straight line</em> for too long.</p>
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<p>Fortunately, the Elves here have a map (your puzzle input) that uses traffic patterns, ambient temperature, and hundreds of other parameters to calculate exactly how much heat loss can be expected for a crucible entering any particular city block.</p>
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<p>For example:</p>
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<pre><code>2413432311323
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3215453535623
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3255245654254
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3446585845452
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4546657867536
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1438598798454
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4457876987766
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3637877979653
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4654967986887
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4564679986453
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1224686865563
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2546548887735
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4322674655533
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</code></pre>
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<p>Each city block is marked by a single digit that represents the <em>amount of heat loss if the crucible enters that block</em>. The starting point, the lava pool, is the top-left city block; the destination, the machine parts factory, is the bottom-right city block. (Because you already start in the top-left block, you don't incur that block's heat loss unless you leave that block and then return to it.)</p>
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<p>Because it is difficult to keep the top-heavy crucible going in a straight line for very long, it can move <em>at most three blocks</em> in a single direction before it must turn 90 degrees left or right. The crucible also can't reverse direction; after entering each city block, it may only turn left, continue straight, or turn right.</p>
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<p>One way to <em>minimize heat loss</em> is this path:</p>
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<pre><code>2<em>></em><em>></em>34<em>^</em><em>></em><em>></em><em>></em>1323
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32<em>v</em><em>></em><em>></em><em>></em>35<em>v</em>5623
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32552456<em>v</em><em>></em><em>></em>54
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3446585845<em>v</em>52
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4546657867<em>v</em><em>></em>6
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14385987984<em>v</em>4
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44578769877<em>v</em>6
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36378779796<em>v</em><em>></em>
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465496798688<em>v</em>
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456467998645<em>v</em>
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12246868655<em><</em><em>v</em>
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25465488877<em>v</em>5
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43226746555<em>v</em><em>></em>
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</code></pre>
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<p>This path never moves more than three consecutive blocks in the same direction and incurs a heat loss of only <code><em>102</em></code>.</p>
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<p>Directing the crucible from the lava pool to the machine parts factory, but not moving more than three consecutive blocks in the same direction, <em>what is the least heat loss it can incur?</em></p>
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<p>Your puzzle answer was <code>1246</code>.</p><p class="day-success">The first half of this puzzle is complete! It provides one gold star: *</p>
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<article class="day-desc"><h2 id="part2">--- Part Two ---</h2><p>The crucibles of lava simply aren't large enough to provide an adequate supply of lava to the machine parts factory. Instead, the Elves are going to upgrade to <em>ultra crucibles</em>.</p>
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<p>Ultra crucibles are even more difficult to steer than normal crucibles. Not only do they have trouble going in a straight line, but they also have trouble turning!</p>
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<p>Once an ultra crucible starts moving in a direction, it needs to move <em>a minimum of four blocks</em> in that direction before it can turn (or even before it can stop at the end). However, it will eventually start to get wobbly: an ultra crucible can move a maximum of <em>ten consecutive blocks</em> without turning.</p>
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<p>In the above example, an ultra crucible could follow this path to minimize heat loss:</p>
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<pre><code>2<em>></em><em>></em><em>></em><em>></em><em>></em><em>></em><em>></em><em>></em>1323
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32154535<em>v</em>5623
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32552456<em>v</em>4254
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34465858<em>v</em>5452
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45466578<em>v</em><em>></em><em>></em><em>></em><em>></em>
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143859879845<em>v</em>
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445787698776<em>v</em>
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363787797965<em>v</em>
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465496798688<em>v</em>
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456467998645<em>v</em>
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122468686556<em>v</em>
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254654888773<em>v</em>
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432267465553<em>v</em>
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</code></pre>
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<p>In the above example, an ultra crucible would incur the minimum possible heat loss of <code><em>94</em></code>.</p>
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<p>Here's another example:</p>
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<pre><code>111111111111
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999999999991
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999999999991
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999999999991
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999999999991
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</code></pre>
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<p>Sadly, an ultra crucible would need to take an unfortunate path like this one:</p>
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<pre><code>1<em>></em><em>></em><em>></em><em>></em><em>></em><em>></em><em>></em>1111
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9999999<em>v</em>9991
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9999999<em>v</em>9991
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9999999<em>v</em>9991
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9999999<em>v</em><em>></em><em>></em><em>></em><em>></em>
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</code></pre>
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<p>This route causes the ultra crucible to incur the minimum possible heat loss of <code><em>71</em></code>.</p>
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<p>Directing the <em>ultra crucible</em> from the lava pool to the machine parts factory, <em>what is the least heat loss it can incur?</em></p>
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