78 lines
2.7 KiB
Markdown
78 lines
2.7 KiB
Markdown
## \-\-- Day 3: Spiral Memory \-\--
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You come across an experimental new kind of memory stored on an
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[infinite two-dimensional
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grid]{title="Good thing we have all these infinite two-dimensional grids lying around!"}.
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Each square on the grid is allocated in a spiral pattern starting at a
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location marked `1` and then counting up while spiraling outward. For
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example, the first few squares are allocated like this:
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17 16 15 14 13
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18 5 4 3 12
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19 6 1 2 11
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20 7 8 9 10
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21 22 23---> ...
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While this is very space-efficient (no squares are skipped), requested
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data must be carried back to square `1` (the location of the only access
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port for this memory system) by programs that can only move up, down,
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left, or right. They always take the shortest path: the [Manhattan
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Distance](https://en.wikipedia.org/wiki/Taxicab_geometry) between the
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location of the data and square `1`.
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For example:
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- Data from square `1` is carried `0` steps, since it\'s at the access
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port.
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- Data from square `12` is carried `3` steps, such as: down, left,
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left.
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- Data from square `23` is carried only `2` steps: up twice.
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- Data from square `1024` must be carried `31` steps.
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*How many steps* are required to carry the data from the square
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identified in your puzzle input all the way to the access port?
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Your puzzle answer was `371`.
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## \-\-- Part Two \-\-- {#part2}
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As a stress test on the system, the programs here clear the grid and
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then store the value `1` in square `1`. Then, in the same allocation
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order as shown above, they store the sum of the values in all adjacent
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squares, including diagonals.
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So, the first few squares\' values are chosen as follows:
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- Square `1` starts with the value `1`.
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- Square `2` has only one adjacent filled square (with value `1`), so
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it also stores `1`.
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- Square `3` has both of the above squares as neighbors and stores the
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sum of their values, `2`.
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- Square `4` has all three of the aforementioned squares as neighbors
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and stores the sum of their values, `4`.
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- Square `5` only has the first and fourth squares as neighbors, so it
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gets the value `5`.
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Once a square is written, its value does not change. Therefore, the
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first few squares would receive the following values:
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147 142 133 122 59
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304 5 4 2 57
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330 10 1 1 54
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351 11 23 25 26
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362 747 806---> ...
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What is the *first value written* that is *larger* than your puzzle
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input?
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Your puzzle answer was `369601`.
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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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Your puzzle input was `368078`{.puzzle-input}.
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