Advent Of Code

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Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2023

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🦶️ - 2023 DAY 21 SOLUTIONS - 🦶️ (programming.dev)

submitted 8 months ago* (last edited 8 months ago) by [email protected] to c/[email protected]

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Day 21: Step

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[–] [email protected] 1 points 8 months ago* (last edited 8 months ago)

My part 2 solution assumes the input has an unimpeded shortest path from the center of each garden section to its corner, and to the center of its neighbor. The possible destinations will form a diamond pattern, with "radius" equal to the number of steps. I broke down the possible section permutations:

Sections that are completely within the interior of the diamond
- Even number of sections away from the starting section
- Odd number of sections away from the starting section
Sections containing the points of the diamond
Depending on the number of steps, there may be sections adjacent to the point sections, that have two corners outside of the diamond
Edge sections. These will form a zig-zag pattern to cover the diamond boundary.
- "Near" edge sections. These are the parts of the zig-zag nearer to the center of the diamond.
- "Far" edge sections. These won't occur if the edge of the diamond passes perfectly through the corners of the near edge sections.

I determined how many of each of these should be present based on the number of steps, used my code from part 1 to get a destination count for each type, and then added them all up.