2022 Day 14 Complete!
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Advent of Code
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br0xen (AoC++) 28*
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--- Day 14: Regolith Reservoir ---
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The distress signal leads you to a giant waterfall! Actually, hang on - the signal seems like it's coming from the
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waterfall itself, and that doesn't make any sense. However, you do notice a little path that leads behind the waterfall.
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Correction: the distress signal leads you behind a giant waterfall! There seems to be a large cave system here, and the
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signal definitely leads further inside.
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As you begin to make your way deeper underground, you feel the ground rumble for a moment. Sand begins pouring into the
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cave! If you don't quickly figure out where the sand is going, you could quickly become trapped!
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Fortunately, your familiarity with analyzing the path of falling material will come in handy here. You scan a
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two-dimensional vertical slice of the cave above you (your puzzle input) and discover that it is mostly air with
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structures made of rock.
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Your scan traces the path of each solid rock structure and reports the x,y coordinates that form the shape of the path,
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where x represents distance to the right and y represents distance down. Each path appears as a single line of text in
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your scan. After the first point of each path, each point indicates the end of a straight horizontal or vertical line to
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be drawn from the previous point. For example:
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498,4 -> 498,6 -> 496,6
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503,4 -> 502,4 -> 502,9 -> 494,9
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This scan means that there are two paths of rock; the first path consists of two straight lines, and the second path
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consists of three straight lines. (Specifically, the first path consists of a line of rock from 498,4 through 498,6 and
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another line of rock from 498,6 through 496,6.)
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The sand is pouring into the cave from point 500,0.
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Drawing rock as #, air as ., and the source of the sand as +, this becomes:
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4 5 5
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9 0 0
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4 0 3
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0 ......+...
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1 ..........
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2 ..........
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3 ..........
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4 ....#...##
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5 ....#...#.
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6 ..###...#.
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7 ........#.
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8 ........#.
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9 #########.
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Sand is produced one unit at a time, and the next unit of sand is not produced until the previous unit of sand comes to
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rest. A unit of sand is large enough to fill one tile of air in your scan.
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A unit of sand always falls down one step if possible. If the tile immediately below is blocked (by rock or sand), the
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unit of sand attempts to instead move diagonally one step down and to the left. If that tile is blocked, the unit of
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sand attempts to instead move diagonally one step down and to the right. Sand keeps moving as long as it is able to do
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so, at each step trying to move down, then down-left, then down-right. If all three possible destinations are blocked,
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the unit of sand comes to rest and no longer moves, at which point the next unit of sand is created back at the source.
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So, drawing sand that has come to rest as o, the first unit of sand simply falls straight down and then stops:
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......+...
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..........
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..........
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..........
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....#...##
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....#...#.
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..###...#.
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........#.
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......o.#.
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#########.
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The second unit of sand then falls straight down, lands on the first one, and then comes to rest to its left:
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......+...
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..........
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..........
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..........
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....#...##
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....#...#.
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..###...#.
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........#.
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.....oo.#.
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#########.
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After a total of five units of sand have come to rest, they form this pattern:
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......+...
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..........
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..........
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..........
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....#...##
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....#...#.
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..###...#.
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......o.#.
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....oooo#.
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#########.
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After a total of 22 units of sand:
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......+...
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..........
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......o...
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.....ooo..
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....#ooo##
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....#ooo#.
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..###ooo#.
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....oooo#.
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...ooooo#.
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#########.
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Finally, only two more units of sand can possibly come to rest:
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......+...
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..........
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......o...
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.....ooo..
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....#ooo##
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...o#ooo#.
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..###ooo#.
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....oooo#.
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.o.ooooo#.
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#########.
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Once all 24 units of sand shown above have come to rest, all further sand flows out the bottom, falling into the endless
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void. Just for fun, the path any new sand takes before falling forever is shown here with ~:
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.......+...
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.......~...
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......~o...
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.....~ooo..
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....~#ooo##
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...~o#ooo#.
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..~###ooo#.
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..~..oooo#.
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.~o.ooooo#.
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~#########.
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~..........
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~..........
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~..........
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Using your scan, simulate the falling sand. How many units of sand come to rest before sand starts flowing into the
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abyss below?
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Your puzzle answer was 757.
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--- Part Two ---
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You realize you misread the scan. There isn't an endless void at the bottom of the scan - there's floor, and you're
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standing on it!
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You don't have time to scan the floor, so assume the floor is an infinite horizontal line with a y coordinate equal to
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two plus the highest y coordinate of any point in your scan.
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In the example above, the highest y coordinate of any point is 9, and so the floor is at y=11. (This is as if your scan
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contained one extra rock path like -infinity,11 -> infinity,11.) With the added floor, the example above now looks like
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this:
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...........+........
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....................
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....................
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....................
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.........#...##.....
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.........#...#......
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.......###...#......
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.............#......
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.............#......
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.....#########......
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....................
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<-- etc #################### etc -->
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To find somewhere safe to stand, you'll need to simulate falling sand until a unit of sand comes to rest at 500,0,
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blocking the source entirely and stopping the flow of sand into the cave. In the example above, the situation finally
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looks like this after 93 units of sand come to rest:
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............o............
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...........ooo...........
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..........ooooo..........
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.........ooooooo.........
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........oo#ooo##o........
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.......ooo#ooo#ooo.......
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......oo###ooo#oooo......
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.....oooo.oooo#ooooo.....
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....oooooooooo#oooooo....
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...ooo#########ooooooo...
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..ooooo.......ooooooooo..
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#########################
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Using your scan, simulate the falling sand until the source of the sand becomes blocked. How many units of sand come to
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rest?
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Your puzzle answer was 24943.
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Both parts of this puzzle are complete! They provide two gold stars: **
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2022/about
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. https://adventofcode.com/2022/events
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. https://adventofcode.com/2022/settings
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. https://adventofcode.com/2022/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2022/support
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. https://adventofcode.com/2022
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. https://adventofcode.com/2022
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. https://adventofcode.com/2022/support
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. https://adventofcode.com/2022/sponsors
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. https://adventofcode.com/2022/leaderboard
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. https://adventofcode.com/2022/stats
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. https://adventofcode.com/2022/sponsors
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. https://adventofcode.com/2018/day/17
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. https://adventofcode.com/2022
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. https://adventofcode.com/2022/day/14/input
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