56 lines
2 KiB
C#
56 lines
2 KiB
C#
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// TODO: I've shamelessly copied this off Reddit because i had no idea how to solve it.
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// I need to come back to this and actually solve this myself.
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/*using var sr = new StreamReader("./day05.txt");
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var input = sr.ReadToEnd().Split("\n").Select(x => x.Trim());
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foreach (var line in input)
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{
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var nums = line.Split(", ->".ToArray(), StringSplitOptions.RemoveEmptyEntries).Select(byte.Parse).ToArray();
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var start = new Vector2(nums[0], nums[1]);
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var end = new Vector2(nums[2], nums[3]);
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}*/
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using var sr = new StreamReader("../inputs/day05.txt");
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var input = sr.ReadToEnd();
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Console.WriteLine(GetIntersectionCount(ParseLines(input, skipDiagonals: true)));
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Console.WriteLine(GetIntersectionCount(ParseLines(input, skipDiagonals: false)));
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private static int GetIntersectionCount(IEnumerable<IEnumerable<Vec2>> lines)
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{
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// build a grid with iterating over all points, counting intersections:
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var grid = new Dictionary<Vec2, int>();
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foreach (var pt in lines.SelectMany(pt => pt))
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{
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grid[pt] = grid.GetValueOrDefault(pt, 0) + 1;
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}
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return grid.Count(kvp => kvp.Value > 1);
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}
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private static IEnumerable<IEnumerable<Vec2>> ParseLines(string input, bool skipDiagonals) =>
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from line in input.Split("\n")
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// parse the numbers first:
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let ns = (
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from st in line.Split(", ->".ToArray(), StringSplitOptions.RemoveEmptyEntries)
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select int.Parse(st)
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).ToArray()
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// line properties:
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let start = new Vec2(ns[0], ns[1])
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let end = new Vec2(ns[2], ns[3])
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let displacement = new Vec2(end.x - start.x, end.y - start.y)
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let length = 1 + Math.Max(Math.Abs(displacement.x), Math.Abs(displacement.y))
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let dir = new Vec2(Math.Sign(displacement.x), Math.Sign(displacement.y))
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// represent lines with a set of points:
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let points =
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from i in Enumerable.Range(0, length)
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select new Vec2(start.x + i * dir.x, start.y + i * dir.y)
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where !skipDiagonals || dir.x == 0 || dir.y == 0 // skip diagonals in part 1
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select points;
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record Vec2(int x, int y);
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