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Day 13 optimized and fixed

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This fixes my logic errors from the first attempt so the letters are much clearer now. It also swaps from trying to iterate over segments of a grid, pulling from later segments, to simply storing the list of marked points in a more efficient (and obviously smaller) collection that we add to and remove from when transforming points via folding, which is where the speedup comes from.

Fun fact: printing the result is about a quarter of the runtime of part 2.
This commit is contained in:
Chris Pickett
2021-12-13 08:48:37 -06:00
parent 4b9ff1c4bd
commit 4fc4bd2c20
1 changed files with 39 additions and 116 deletions
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155
src/13.cs
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@ -8,7 +8,7 @@ internal class Day13 : Day
Logger.Log("-----");
var lines = File.ReadAllLines("inputs/13.txt");
int phase = 0;
var points = new List<(int, int)>();
var points = new HashSet<(int, int)>();
var folds = new List<(char, int)>();
foreach (var line in lines)
{
@ -29,145 +29,68 @@ internal class Day13 : Day
folds.Add((instruction[0].Last(), Convert.ToInt32(instruction[1])));
}
}
var grid = new bool[points.Max(x => x.Item1) + 1, points.Max(x => x.Item2) + 1];
foreach (var point in points)
{
grid[point.Item1, point.Item2] = true;
}
Part1(grid, folds);
Part2(grid, folds);
Part1(points, folds);
Part2(points, folds);
Logger.Log("");
}
private static void Part1(bool[,] grid, IEnumerable<(char, int)> folds)
private static void Fold(ICollection<(int x, int y)> points, char axis, int line)
{
using var t = new Timer();
int maxX = grid.GetLength(0);
int maxY = grid.GetLength(1);
foreach (var fold in folds)
if (axis == 'x')
{
for (int i = 0; i < grid.GetLength(0); i++)
points.Where(x => x.y > line).ToList().ForEach(x =>
{
for (int j = 0; j < grid.GetLength(1); j++)
{
var newX = i;
var newY = j;
if (fold.Item1 == 'y' && newX > fold.Item2)
{
newX = maxX - 1 - i;
}
if (fold.Item1 == 'x' && newY > fold.Item2)
{
newY = maxY - 1 - j;
}
if (grid[i,j])
{
grid[newX, newY] = grid[i, j];
}
}
}
if (fold.Item1 == 'x')
{
maxY -= fold.Item2 + 1;
}
else if (fold.Item1 == 'y')
{
maxX -= fold.Item2 + 1;
}
break;
points.Add((x.x, x.y - (x.y - line) * 2));
points.Remove(x);
});
}
int numDots = 0;
for (int i = 0; i < maxX; i++)
else
{
for (int j = 0; j < maxY; j++)
points.Where(x => x.x > line).ToList().ForEach(x =>
{
if (grid[i, j] == true)
{
numDots++;
}
}
points.Add((x.x - (x.x - line) * 2, x.y));
points.Remove(x);
});
}
Logger.Log($"part1: {numDots}");
}
private static void Part2(bool[,] grid, IEnumerable<(char, int)> folds)
private static void Part1(ICollection<(int x, int y)> grid, IList<(char axis, int line)> folds)
{
using var t = new Timer();
int maxX = grid.GetLength(0);
int maxY = grid.GetLength(1);
Fold(grid, folds[0].axis, folds[0].line);
for (int foldNum = 0; foldNum < folds.Count(); foldNum++)
Logger.Log($"part1: {grid.Count}");
}
private static void Part2(ICollection<(int x, int y)> grid, IList<(char axis, int line)> folds)
{
using var t = new Timer();
folds.Skip(1).ForEach(x => Fold(grid, x.axis, x.line));
int maxX = grid.Max(x => x.x);
int maxY = grid.Max(x => x.y);
var sb = new System.Text.StringBuilder();
for (int i = 0; i <= maxX; i++)
{
var fold = folds.ElementAt(foldNum);
if (foldNum > 0)
for (int j = 0; j <= maxY; j++)
{
var iStart = 0;
var jStart = 0;
if (fold.Item1 == 'x')
if (grid.Contains((i, j)))
{
jStart = fold.Item2 + 1;
}
if (fold.Item1 == 'y')
{
iStart = fold.Item2 + 1;
}
for (int i = iStart; i < maxX; i++)
{
for (int j = jStart; j < maxY; j++)
{
var newX = i;
var newY = j;
if (fold.Item1 == 'y' && newX > fold.Item2)
{
newX = maxX - 1 - i;
}
if (fold.Item1 == 'x' && newY > fold.Item2)
{
newY = maxY - 1 - j;
}
if (grid[i, j])
{
grid[newX, newY] = grid[i, j];
}
}
}
}
if (fold.Item1 == 'x')
{
maxY -= fold.Item2 + 1;
}
else if (fold.Item1 == 'y')
{
maxX -= fold.Item2 + 1;
}
}
int numDots = 0;
for (int i = 0; i < maxX; i++)
{
for (int j = 0; j < maxY; j++)
{
if (grid[i, j] == true)
{
Console.Write("#");
numDots++;
sb.Append('#');
}
else
{
Console.Write(".");
sb.Append('.');
}
}
Console.WriteLine();
if (i < maxX)
{
sb.Append('\n');
}
}
Logger.Log($"part2: {numDots}");
Logger.Log(sb.ToString());
Logger.Log($"part2: {grid.Count}");
}
}