2022 Day 24 Complete

2022/day24/problem

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+   br0xen (AoC++) 41*
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+                          int y=2022;
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+
+--- Day 24: Blizzard Basin ---
+
+   With everything replanted for next year (and with
+   elephants and monkeys to tend the grove), you and the
+   Elves leave for the extraction point.
+
+   Partway up the mountain that shields the grove is a
+   flat, open area that serves as the extraction point.
+   It's a bit of a climb, but nothing the expedition can't
+   handle.
+
+   At least, that would normally be true; now that the
+   mountain is covered in snow, things have become more
+   difficult than the Elves are used to.
+
+   As the expedition reaches a valley that must be
+   traversed to reach the extraction site, you find that
+   strong, turbulent winds are pushing small blizzards of
+   snow and sharp ice around the valley. It's a good thing
+   everyone packed warm clothes! To make it across safely,
+   you'll need to find a way to avoid them.
+
+   Fortunately, it's easy to see all of this from the
+   entrance to the valley, so you make a map of the valley
+   and the blizzards (your puzzle input). For example:
+
+ #.#####
+ #.....#
+ #>....#
+ #.....#
+ #...v.#
+ #.....#
+ #####.#
+
+   The walls of the valley are drawn as #; everything else
+   is ground. Clear ground - where there is currently no
+   blizzard - is drawn as .. Otherwise, blizzards are
+   drawn with an arrow indicating their direction of
+   motion: up (^), down (v), left (<), or right (>).
+
+   The above map includes two blizzards, one moving right
+   (>) and one moving down (v). In one minute, each
+   blizzard moves one position in the direction it is
+   pointing:
+
+ #.#####
+ #.....#
+ #.>...#
+ #.....#
+ #.....#
+ #...v.#
+ #####.#
+
+   Due to conservation of blizzard energy, as a blizzard
+   reaches the wall of the valley, a new blizzard forms on
+   the opposite side of the valley moving in the same
+   direction. After another minute, the bottom
+   downward-moving blizzard has been replaced with a new
+   downward-moving blizzard at the top of the valley
+   instead:
+
+ #.#####
+ #...v.#
+ #..>..#
+ #.....#
+ #.....#
+ #.....#
+ #####.#
+
+   Because blizzards are made of tiny snowflakes, they
+   pass right through each other. After another minute,
+   both blizzards temporarily occupy the same position,
+   marked 2:
+
+ #.#####
+ #.....#
+ #...2.#
+ #.....#
+ #.....#
+ #.....#
+ #####.#
+
+   After another minute, the situation resolves itself,
+   giving each blizzard back its personal space:
+
+ #.#####
+ #.....#
+ #....>#
+ #...v.#
+ #.....#
+ #.....#
+ #####.#
+
+   Finally, after yet another minute, the rightward-facing
+   blizzard on the right is replaced with a new one on the
+   left facing the same direction:
+
+ #.#####
+ #.....#
+ #>....#
+ #.....#
+ #...v.#
+ #.....#
+ #####.#
+
+   This process repeats at least as long as you are
+   observing it, but probably forever.
+
+   Here is a more complex example:
+
+ #.######
+ #>>.<^<#
+ #.<..<<#
+ #>v.><>#
+ #<^v^^>#
+ ######.#
+
+   Your expedition begins in the only non-wall position in
+   the top row and needs to reach the only non-wall
+   position in the bottom row. On each minute, you can
+   move up, down, left, or right, or you can wait in
+   place. You and the blizzards act simultaneously, and
+   you cannot share a position with a blizzard.
+
+   In the above example, the fastest way to reach your
+   goal requires 18 steps. Drawing the position of the
+   expedition as E, one way to achieve this is:
+
+ Initial state:
+ #E######
+ #>>.<^<#
+ #.<..<<#
+ #>v.><>#
+ #<^v^^>#
+ ######.#
+
+ Minute 1, move down:
+ #.######
+ #E>3.<.#
+ #<..<<.#
+ #>2.22.#
+ #>v..^<#
+ ######.#
+
+ Minute 2, move down:
+ #.######
+ #.2>2..#
+ #E^22^<#
+ #.>2.^>#
+ #.>..<.#
+ ######.#
+
+ Minute 3, wait:
+ #.######
+ #<^<22.#
+ #E2<.2.#
+ #><2>..#
+ #..><..#
+ ######.#
+
+ Minute 4, move up:
+ #.######
+ #E<..22#
+ #<<.<..#
+ #<2.>>.#
+ #.^22^.#
+ ######.#
+
+ Minute 5, move right:
+ #.######
+ #2Ev.<>#
+ #<.<..<#
+ #.^>^22#
+ #.2..2.#
+ ######.#
+
+ Minute 6, move right:
+ #.######
+ #>2E<.<#
+ #.2v^2<#
+ #>..>2>#
+ #<....>#
+ ######.#
+
+ Minute 7, move down:
+ #.######
+ #.22^2.#
+ #<vE<2.#
+ #>>v<>.#
+ #>....<#
+ ######.#
+
+ Minute 8, move left:
+ #.######
+ #.<>2^.#
+ #.E<<.<#
+ #.22..>#
+ #.2v^2.#
+ ######.#
+
+ Minute 9, move up:
+ #.######
+ #<E2>>.#
+ #.<<.<.#
+ #>2>2^.#
+ #.v><^.#
+ ######.#
+
+ Minute 10, move right:
+ #.######
+ #.2E.>2#
+ #<2v2^.#
+ #<>.>2.#
+ #..<>..#
+ ######.#
+
+ Minute 11, wait:
+ #.######
+ #2^E^2>#
+ #<v<.^<#
+ #..2.>2#
+ #.<..>.#
+ ######.#
+
+ Minute 12, move down:
+ #.######
+ #>>.<^<#
+ #.<E.<<#
+ #>v.><>#
+ #<^v^^>#
+ ######.#
+
+ Minute 13, move down:
+ #.######
+ #.>3.<.#
+ #<..<<.#
+ #>2E22.#
+ #>v..^<#
+ ######.#
+
+ Minute 14, move right:
+ #.######
+ #.2>2..#
+ #.^22^<#
+ #.>2E^>#
+ #.>..<.#
+ ######.#
+
+ Minute 15, move right:
+ #.######
+ #<^<22.#
+ #.2<.2.#
+ #><2>E.#
+ #..><..#
+ ######.#
+
+ Minute 16, move right:
+ #.######
+ #.<..22#
+ #<<.<..#
+ #<2.>>E#
+ #.^22^.#
+ ######.#
+
+ Minute 17, move down:
+ #.######
+ #2.v.<>#
+ #<.<..<#
+ #.^>^22#
+ #.2..2E#
+ ######.#
+
+ Minute 18, move down:
+ #.######
+ #>2.<.<#
+ #.2v^2<#
+ #>..>2>#
+ #<....>#
+ ######E#
+
+   What is the fewest number of minutes required to avoid
+   the blizzards and reach the goal?
+
+   Your puzzle answer was 240.
+
+--- Part Two ---
+
+   As the expedition reaches the far side of the valley,
+   one of the Elves looks especially dismayed:
+
+   He forgot his snacks at the entrance to the valley!
+
+   Since you're so good at dodging blizzards, the Elves
+   humbly request that you go back for his snacks. From
+   the same initial conditions, how quickly can you make
+   it from the start to the goal, then back to the start,
+   then back to the goal?
+
+   In the above example, the first trip to the goal takes
+   18 minutes, the trip back to the start takes 23
+   minutes, and the trip back to the goal again takes 13
+   minutes, for a total time of 54 minutes.
+
+   What is the fewest number of minutes required to reach
+   the goal, go back to the start, then reach the goal
+   again?
+
+   Your puzzle answer was 717.
+
+   Both parts of this puzzle are complete! They provide
+   two gold stars: **
+
+   At this point, you should return to your Advent
+   calendar and try another puzzle.
+
+   If you still want to see it, you can get your puzzle
+   input.
+
+   You can also [Shareon Twitter Mastodon] this puzzle.
+
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