125 lines
4.4 KiB
Plaintext
125 lines
4.4 KiB
Plaintext
Advent of Code
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--- Day 3: Crossed Wires ---
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The gravity assist was successful, and you're well on your way to the Venus refuelling station. During the rush
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back on Earth, the fuel management system wasn't completely installed, so that's next on the priority list.
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Opening the front panel reveals a jumble of wires. Specifically, two wires are connected to a central port and
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extend outward on a grid. You trace the path each wire takes as it leaves the central port, one wire per line of
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text (your puzzle input).
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The wires twist and turn, but the two wires occasionally cross paths. To fix the circuit, you need to find the
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intersection point closest to the central port. Because the wires are on a grid, use the Manhattan distance for
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this measurement. While the wires do technically cross right at the central port where they both start, this point
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does not count, nor does a wire count as crossing with itself.
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For example, if the first wire's path is R8,U5,L5,D3, then starting from the central port (o), it goes right 8, up
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5, left 5, and finally down 3:
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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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Then, if the second wire's path is U7,R6,D4,L4, it goes up 7, right 6, down 4, and left 4:
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...........
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.+-----+...
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.|.....|...
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.|..+--X-+.
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.|..|..|.|.
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.|.-X--+.|.
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.|..|....|.
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.|.......|.
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.o-------+.
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...........
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These wires cross at two locations (marked X), but the lower-left one is closer to the central port: its distance
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is 3 + 3 = 6.
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Here are a few more examples:
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• R75,D30,R83,U83,L12,D49,R71,U7,L72
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U62,R66,U55,R34,D71,R55,D58,R83 = distance 159
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• R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
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U98,R91,D20,R16,D67,R40,U7,R15,U6,R7 = distance 135
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What is the Manhattan distance from the central port to the closest intersection?
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Your puzzle answer was 258.
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--- Part Two ---
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It turns out that this circuit is very timing-sensitive; you actually need to minimize the signal delay.
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To do this, calculate the number of steps each wire takes to reach each intersection; choose the intersection
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where the sum of both wires' steps is lowest. If a wire visits a position on the grid multiple times, use the
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steps value from the first time it visits that position when calculating the total value of a specific
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intersection.
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The number of steps a wire takes is the total number of grid squares the wire has entered to get to that location,
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including the intersection being considered. Again consider the example from above:
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...........
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.+-----+...
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.|.....|...
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.|..+--X-+.
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.|..|..|.|.
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.|.-X--+.|.
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.|..|....|.
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.|.......|.
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.o-------+.
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...........
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In the above example, the intersection closest to the central port is reached after 8+5+5+2 = 20 steps by the
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first wire and 7+6+4+3 = 20 steps by the second wire for a total of 20+20 = 40 steps.
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However, the top-right intersection is better: the first wire takes only 8+5+2 = 15 and the second wire takes only
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7+6+2 = 15, a total of 15+15 = 30 steps.
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Here are the best steps for the extra examples from above:
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• R75,D30,R83,U83,L12,D49,R71,U7,L72
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U62,R66,U55,R34,D71,R55,D58,R83 = 610 steps
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• R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
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U98,R91,D20,R16,D67,R40,U7,R15,U6,R7 = 410 steps
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What is the fewest combined steps the wires must take to reach an intersection?
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Your puzzle answer was 12304.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another puzzle.
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If you still want to see it, you can get your puzzle input.
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References
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Visible links
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. https://adventofcode.com/
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. Advent of Code Supporter
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https://adventofcode.com/2019/support
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. https://en.wikipedia.org/wiki/Taxicab_geometry
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. https://adventofcode.com/2019
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. https://adventofcode.com/2019/day/3/input
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