59 lines
2.9 KiB
Markdown
Executable File
59 lines
2.9 KiB
Markdown
Executable File
## \-\-\- Day 17: Clumsy Crucible ---
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The lava starts flowing rapidly once the Lava Production Facility is operational. As you leave, the reindeer offers you a parachute, allowing you to quickly reach Gear Island.
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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!
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You land near the gradually-filling pool of lava at the base of your new _lavafall_. Lavaducts will eventually carry the lava throughout the city, but to make use of it immediately, Elves are loading it into large [crucibles](https://en.wikipedia.org/wiki/Crucible) on wheels.
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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.
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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 _from the lava pool to the machine parts factory_. To do this, you need to minimize _heat loss_ while choosing a route that doesn't require the crucible to go in a _straight line_ for too long.
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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.
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For example:
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```
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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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```
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Each city block is marked by a single digit that represents the _amount of heat loss if the crucible enters that block_. 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.)
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Because it is difficult to keep the top-heavy crucible going in a straight line for very long, it can move _at most three blocks_ 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.
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One way to _minimize heat loss_ is this path:
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```
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2>>34^>>>1323
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32v>>>35v5623
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32552456v>>54
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3446585845v52
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4546657867v>6
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14385987984v4
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44578769877v6
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36378779796v>
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465496798688v
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456467998645v
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12246868655<v
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25465488877v5
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43226746555v>
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```
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This path never moves more than three consecutive blocks in the same direction and incurs a heat loss of only `102`.
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Directing the crucible from the lava pool to the machine parts factory, but not moving more than three consecutive blocks in the same direction, _what is the least heat loss it can incur?_ |