57 lines
2.0 KiB
Markdown
57 lines
2.0 KiB
Markdown
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## \-\-- Day 3: Perfectly Spherical Houses in a Vacuum \-\--
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Santa is delivering presents to an infinite two-dimensional grid of
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houses.
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He begins by delivering a present to the house at his starting location,
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and then an elf at the North Pole calls him via radio and tells him
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where to move next. Moves are always exactly one house to the north
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(`^`), south (`v`), east (`>`), or west (`<`). After each move, he
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delivers another present to the house at his new location.
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However, the elf back at the north pole has had a little too much
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eggnog, and so his directions are a little off, and Santa ends up
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visiting some houses more than once. How many houses receive *at least
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one present*?
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For example:
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- `>` delivers presents to `2` houses: one at the starting location,
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and one to the east.
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- `^>v<` delivers presents to `4` houses in a square, including twice
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to the house at his starting/ending location.
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- `^v^v^v^v^v` delivers a bunch of presents to some very lucky
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children at only `2` houses.
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## \-\-- Part Two \-\-- {#part2}
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The next year, to speed up the process, Santa creates a robot version of
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himself, *Robo-Santa*, to deliver presents with him.
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Santa and Robo-Santa start at the same location (delivering two presents
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to the same starting house), then take turns moving based on
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instructions from the elf, who is
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eggnoggedly
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reading from the same script as the previous year.
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This year, how many houses receive *at least one present*?
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For example:
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- `^v` delivers presents to `3` houses, because Santa goes north, and
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then Robo-Santa goes south.
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- `^>v<` now delivers presents to `3` houses, and Santa and Robo-Santa
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end up back where they started.
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- `^v^v^v^v^v` now delivers presents to `11` houses, with Santa going
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one direction and Robo-Santa going the other.
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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](/2015) 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](3/input).
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