264 lines
7.8 KiB
Plaintext
264 lines
7.8 KiB
Plaintext
Advent of Code
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--- Day 22: Sporifica Virus ---
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Diagnostics indicate that the local grid computing cluster has been
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contaminated with the Sporifica Virus. The grid computing cluster is a
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seemingly-infinite two-dimensional grid of compute nodes. Each node is either
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clean or infected by the virus.
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To prevent overloading the nodes (which would render them useless to the
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virus) or detection by system administrators, exactly one virus carrier moves
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through the network, infecting or cleaning nodes as it moves. The virus
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carrier is always located on a single node in the network (the current node)
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and keeps track of the direction it is facing.
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To avoid detection, the virus carrier works in bursts; in each burst, it
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wakes up, does some work, and goes back to sleep. The following steps are all
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executed in order one time each burst:
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* If the current node is infected, it turns to its right. Otherwise, it
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turns to its left. (Turning is done in-place; the current node does not
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change.)
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* If the current node is clean, it becomes infected. Otherwise, it becomes
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cleaned. (This is done after the node is considered for the purposes of
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changing direction.)
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* The virus carrier moves forward one node in the direction it is facing.
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Diagnostics have also provided a map of the node infection status (your
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puzzle input). Clean nodes are shown as .; infected nodes are shown as #.
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This map only shows the center of the grid; there are many more nodes beyond
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those shown, but none of them are currently infected.
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The virus carrier begins in the middle of the map facing up.
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For example, suppose you are given a map like this:
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..#
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#..
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...
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Then, the middle of the infinite grid looks like this, with the virus
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carrier's position marked with [ ]:
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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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The virus carrier is on a clean node, so it turns left, infects the node, and
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moves 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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The virus carrier is on an infected node, so it turns right, cleans the node,
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and moves up:
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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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Four times in a row, the virus carrier finds a clean, infects it, turns left,
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and moves forward, ending in the same place and still facing up:
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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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Now on the same node as before, it sees an infection, which causes it to turn
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right, clean the node, and move forward:
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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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After the above actions, a total of 7 bursts of activity had taken place. Of
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them, 5 bursts of activity caused an infection.
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After a total of 70, the grid looks like this, with the virus carrier facing
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up:
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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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By this time, 41 bursts of activity caused an infection (though most of those
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nodes have since been cleaned).
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After a total of 10000 bursts of activity, 5587 bursts will have caused an
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infection.
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Given your actual map, after 10000 bursts of activity, how many bursts cause
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a node to become infected? (Do not count nodes that begin infected.)
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Your puzzle answer was 5348.
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The first half of this puzzle is complete! It provides one gold star: *
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--- Part Two ---
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As you go to remove the virus from the infected nodes, it evolves to resist
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your attempt.
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Now, before it infects a clean node, it will weaken it to disable your
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defenses. If it encounters an infected node, it will instead flag the node to
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be cleaned in the future. So:
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* Clean nodes become weakened.
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* Weakened nodes become infected.
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* Infected nodes become flagged.
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* Flagged nodes become clean.
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Every node is always in exactly one of the above states.
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The virus carrier still functions in a similar way, but now uses the
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following logic during its bursts of action:
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* Decide which way to turn based on the current node:
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* If it is clean, it turns left.
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* If it is weakened, it does not turn, and will continue moving in the
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same direction.
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* If it is infected, it turns right.
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* If it is flagged, it reverses direction, and will go back the way it
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came.
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* Modify the state of the current node, as described above.
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* The virus carrier moves forward one node in the direction it is facing.
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Start with the same map (still using . for clean and # for infected) and
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still with the virus carrier starting in the middle and facing up.
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Using the same initial state as the previous example, and drawing weakened as
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W and flagged as F, the middle of the infinite grid looks like this, with the
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virus carrier's position again marked with [ ]:
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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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This is the same as before, since no initial nodes are weakened or flagged.
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The virus carrier is on a clean node, so it still turns left, instead weakens
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the node, and moves left:
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . # . . .
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. . .[#]W . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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The virus carrier is on an infected node, so it still turns right, instead
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flags the node, and moves up:
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . .[.]. # . . .
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. . . F W . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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This process repeats three more times, ending on the previously-flagged node
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and facing right:
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . W W . # . . .
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. . W[F]W . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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Finding a flagged node, it reverses direction and cleans the node:
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . W W . # . . .
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. .[W]. W . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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The weakened node becomes infected, and it continues in the same direction:
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . W W . # . . .
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.[.]# . W . . . .
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. . . . . . . . .
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. . . . . . . . .
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. . . . . . . . .
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Of the first 100 bursts, 26 will result in infection. Unfortunately, another
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feature of this evolved virus is speed; of the first 10000000 bursts, 2511944
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will result in infection.
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Given your actual map, after 10000000 bursts of activity, how many bursts
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cause a node to become infected? (Do not count nodes that begin infected.)
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Although it hasn't changed, you can still get your puzzle input.
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Answer: 2512225
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References
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Visible links
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. https://en.wikipedia.org/wiki/Morris_worm#The_mistake
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. https://www.youtube.com/watch?v=2vj37yeQQHg
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. http://adventofcode.com/2017/day/22/input
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