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Day 12

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This one is sloppier than I'd like, but these visual problems always throw me for a loop anyway. I was lucky I was able to use the ugly "num corners" trick quickly here.
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Chris Pickett
2024-12-12 15:42:03 -06:00
parent 5af2ab5c39
commit 7b968463d6
1 changed files with 210 additions and 0 deletions
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src/12.cs Normal file
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using aoc2024.Util;
namespace aoc2024;
internal class Day12 : Day
{
private char[][] grid = [];
internal override void Parse()
{
var lines = Util.Parsing.ReadAllLines($"{GetDay()}").ToList();
grid = new char[lines.Count][];
for (int y = 0; y < lines.Count; y++)
{
var row = new char[lines[y].Length];
for (int x = 0; x < lines[y].Length; x++)
{
row[x] = lines[y][x];
}
grid[y] = row;
}
}
internal override string Part1()
{
HashSet<ivec2> used = [];
HashSet<(char, HashSet<ivec2>)> plots = [];
for (int y = 0; y < grid.Length; y++)
{
for (int x = 0; x < grid[y].Length; x++)
{
var v = new ivec2(x, y);
if (used.Contains(v))
{
continue;
}
var plot = (grid[y][x], new HashSet<ivec2>());
plots.Add(plot);
var q = new Queue<ivec2>();
q.Enqueue(v);
plot.Item2.Add(v);
while (q.Count > 0)
{
var check = q.Dequeue();
var neighbors = check.GetBoundedOrthogonalNeighbors(0, 0, grid[0].Length - 1, grid.Length - 1);
foreach (var n in neighbors)
{
if (grid[n.y][n.x] == grid[y][x] && !plot.Item2.Contains(n))
{
q.Enqueue(n);
plot.Item2.Add(n);
}
}
}
used.UnionWith(plot.Item2);
}
}
long total = 0;
foreach (var plot in plots)
{
var area = plot.Item2.Count;
var perimeter = 0;
foreach (var plotPt in plot.Item2)
{
perimeter += plotPt.GetOrthogonalNeighbors().Count(pt => !plot.Item2.Contains(pt));
}
var plotTotal = area * perimeter;
total += plotTotal;
}
return $"Area * perimeter cost: <+white>{total}";
}
private bool IsSame(char c, ivec2 pt)
{
if (!pt.IsWithinRange(0, 0, grid[0].Length - 1, grid.Length - 1))
{
return false;
}
return grid[pt.y][pt.x] == c;
}
private int NumCorners(IEnumerable<ivec2> points)
{
int numCorners = 0;
foreach (var pt in points)
{
var ch = grid[pt.y][pt.x];
// convex
{
// top-left
if (!IsSame(ch, pt - new ivec2(1, 0)) &&
!IsSame(ch, pt - new ivec2(0, 1)))
{
numCorners++;
}
// top-right
if (!IsSame(ch, pt + new ivec2(1, 0)) &&
!IsSame(ch, pt - new ivec2(0, 1)))
{
numCorners++;
}
// bottom-left
if (!IsSame(ch, pt - new ivec2(1, 0)) &&
!IsSame(ch, pt + new ivec2(0, 1)))
{
numCorners++;
}
// bottom-right
if (!IsSame(ch, pt + new ivec2(1, 0)) &&
!IsSame(ch, pt + new ivec2(0, 1)))
{
numCorners++;
}
}
// concave
{
// top-left
if (IsSame(ch, pt - new ivec2(1, 0)) &&
IsSame(ch, pt - new ivec2(0, 1)) &&
!IsSame(ch, pt - ivec2.ONE))
{
numCorners++;
}
// top-right
if (IsSame(ch, pt + new ivec2(1, 0)) &&
IsSame(ch, pt - new ivec2(0, 1)) &&
!IsSame(ch, pt + new ivec2(1, -1)))
{
numCorners++;
}
// bottom-left
if (IsSame(ch, pt - new ivec2(1, 0)) &&
IsSame(ch, pt + new ivec2(0, 1)) &&
!IsSame(ch, pt + new ivec2(-1, 1)))
{
numCorners++;
}
// bottom-right
if (IsSame(ch, pt + new ivec2(1, 0)) &&
IsSame(ch, pt + new ivec2(0, 1)) &&
!IsSame(ch, pt + new ivec2(1, 1)))
{
numCorners++;
}
}
}
return numCorners;
}
internal override string Part2()
{
HashSet<ivec2> used = [];
List<(char, HashSet<ivec2>)> plots = [];
for (int y = 0; y < grid.Length; y++)
{
for (int x = 0; x < grid[y].Length; x++)
{
var v = new ivec2(x, y);
if (used.Contains(v))
{
continue;
}
var plot = (grid[y][x], new HashSet<ivec2>());
plots.Add(plot);
var q = new Queue<ivec2>();
q.Enqueue(v);
plot.Item2.Add(v);
while (q.Count > 0)
{
var check = q.Dequeue();
var neighbors = check.GetBoundedOrthogonalNeighbors(0, 0, grid[0].Length - 1, grid.Length - 1);
foreach (var n in neighbors)
{
if (grid[n.y][n.x] != grid[y][x] || plot.Item2.Contains(n))
{
continue;
}
q.Enqueue(n);
plot.Item2.Add(n);
}
}
used.UnionWith(plot.Item2);
}
}
long total = 0;
foreach (var plot in plots)
{
var area = plot.Item2.Count;
var numSides = NumCorners(plot.Item2);
total += area * numSides;
}
return $"Area * sides cost: <+white>{total}";
}
}