81 lines
2.7 KiB
Markdown
81 lines
2.7 KiB
Markdown
## \-\-- Day 12: Digital Plumber \-\--
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Walking along the memory banks of the stream, you find a small village
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that is experiencing a little confusion: some programs can\'t
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communicate with each other.
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Programs in this village communicate using a fixed system of *pipes*.
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Messages are passed between programs using these pipes, but most
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programs aren\'t connected to each other directly. Instead, programs
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pass messages between each other until the message reaches the intended
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recipient.
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For some reason, though, some of these messages aren\'t ever reaching
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their intended recipient, and the programs suspect that some
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pipes
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are missing. They would like you to investigate.
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You walk through the village and record the ID of each program and the
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IDs with which it can communicate directly (your puzzle input). Each
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program has one or more programs with which it can communicate, and
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these pipes are bidirectional; if `8` says it can communicate with `11`,
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then `11` will say it can communicate with `8`.
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You need to figure out how many programs are in the group that contains
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program ID `0`.
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For example, suppose you go door-to-door like a travelling salesman and
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record the following list:
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0 <-> 2
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1 <-> 1
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2 <-> 0, 3, 4
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3 <-> 2, 4
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4 <-> 2, 3, 6
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5 <-> 6
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6 <-> 4, 5
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In this example, the following programs are in the group that contains
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program ID `0`:
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- Program `0` by definition.
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- Program `2`, directly connected to program `0`.
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- Program `3` via program `2`.
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- Program `4` via program `2`.
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- Program `5` via programs `6`, then `4`, then `2`.
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- Program `6` via programs `4`, then `2`.
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Therefore, a total of `6` programs are in this group; all but program
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`1`, which has a pipe that connects it to itself.
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*How many programs* are in the group that contains program ID `0`?
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Your puzzle answer was `113`.
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## \-\-- Part Two \-\-- {#part2}
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There are more programs than just the ones in the group containing
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program ID `0`. The rest of them have no way of reaching that group, and
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still might have no way of reaching each other.
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A *group* is a collection of programs that can all communicate via pipes
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either directly or indirectly. The programs you identified just a moment
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ago are all part of the same group. Now, they would like you to
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determine the total number of groups.
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In the example above, there were `2` groups: one consisting of programs
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`0,2,3,4,5,6`, and the other consisting solely of program `1`.
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*How many groups are there* in total?
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Your puzzle answer was `202`.
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Both parts of this puzzle are complete! They provide two gold stars:
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\*\*
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At this point, you should [return to your Advent calendar](/2017) and
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try another puzzle.
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If you still want to see it, you can [get your puzzle
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input](12/input).
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