mirror of
https://github.com/parnic/advent-of-code-2023.git
synced 2025-06-17 00:51:52 -05:00
Day 21
I solved part 1 the naive way and was reasonably happy with it. I was successfully using that solution with some negative-modulus junk to brute force part 2 (I could get the correct answer for the example data's smaller number of steps), but there was no way it was completing in a reasonable amount of time or without blowing all my RAM. I was at a complete loss for how to solve part 2 the "smart" way, so I learned from this video: https://www.youtube.com/watch?v=9UOMZSL0JTg I understand why this works now, but I was not going to be getting it on my own (nor did I really want to spend the time it would have taken me to attempt to arrive at a similar solution).
This commit is contained in:
@ -73,6 +73,8 @@
|
|||||||
<EmbeddedResource Include="inputs\20.txt" />
|
<EmbeddedResource Include="inputs\20.txt" />
|
||||||
<EmbeddedResource Include="inputs\20a.txt" />
|
<EmbeddedResource Include="inputs\20a.txt" />
|
||||||
<EmbeddedResource Include="inputs\20b.txt" />
|
<EmbeddedResource Include="inputs\20b.txt" />
|
||||||
|
<EmbeddedResource Include="inputs\21.txt" />
|
||||||
|
<EmbeddedResource Include="inputs\21a.txt" />
|
||||||
</ItemGroup>
|
</ItemGroup>
|
||||||
|
|
||||||
<ItemGroup>
|
<ItemGroup>
|
||||||
|
|||||||
131
inputs/21.txt
Normal file
131
inputs/21.txt
Normal file
@ -0,0 +1,131 @@
|
|||||||
|
...................................................................................................................................
|
||||||
|
..#...#....#.......#.#..##......#...............#..#....#......................................#....##.........#...##..#.#.....#...
|
||||||
|
.....#..#............#....#.#...##..#.................#..#..................#...#.#.......#.#..#....#.....#...#.#..............#...
|
||||||
|
.#........#...........#......................#..........#................#...#..............#......#...........#..#.....#.#........
|
||||||
|
..#.#.#..........#.......#....#....#......#.......#...#..................#.###...........#...........##...#..........#.##.#.#.#.#..
|
||||||
|
.#.#.........#.....#.#...........#.......##.###.....#.#.........#.#.........##.................##.........##.#.............##.#....
|
||||||
|
...#.#...#.#...........#.#.####....................##.#........##..........#......#.............##.#...............#...............
|
||||||
|
......##...#.##....#.......#....#...#....#..................................#......#.#.#..#.........#..........#..#...#............
|
||||||
|
.#..#..#...#........................#......#...##.................#...............#..........##.........#..........................
|
||||||
|
......#...#..#...#................#....#.....................#..................#...#.............#..#..#.......##.#.....#.........
|
||||||
|
.#........#..........#...#........#...........##..............#...#..#.................#............................#.....#....#...
|
||||||
|
...............##..####...........###..#...##.#................#.......#.................#......#........................#......#..
|
||||||
|
....#............#.........#...........#..#.#.#..........#..........#...............#....#....###...##.........#...................
|
||||||
|
.#.....#..#....#.#..............#..#.....#.#........................................##..#.....#....#...#..##.##...#................
|
||||||
|
.....#.....#....#..#......#...............#....#.......#..#..............#...................#............................#........
|
||||||
|
................#........#................#.#.........................#.....#.......#.....#.................#.....#.........#......
|
||||||
|
......##....#..#...#....#..#............#....#...........#..##............#..#.........#.......#...#.#..........#.....#...#....#...
|
||||||
|
....#.#...#.........#..#....#...#......#................#..##.......##.................#..#....#..........#......#.................
|
||||||
|
..........#..#..#..#..........#........................#.................###..............##.#..#.#......#...#.##...........#......
|
||||||
|
.###...#.......#..................#....#...............#.......#..#..#...#..#.......................#.#...#..#........#...#......#.
|
||||||
|
.......#...........#.#..##......#................#............#.#.#......#................#.........#.....#..........#..#..#...#...
|
||||||
|
....#.....................##....#......##...................#...............#.....#...............#..#........#.#....##.....#..#...
|
||||||
|
.......#..#.##..#...###...#........#.............##........#......................##.........#...............#....#.#..............
|
||||||
|
..###.......#..#......#........#...#...............###.###.........#.#.#........#...........#.........#...........#....#....#.#....
|
||||||
|
.....#..........#......#...#.........#........#........#...#...........#.....#.#.............................#.#.......###.##.#.##.
|
||||||
|
..#.................#.............#................#.#............#.#.....#........................#........#.................#....
|
||||||
|
.#..##..#.#......##..........................#..#.........#.....#......#.....#.....#............................###.....##....#..#.
|
||||||
|
.......#.#.......#............#...........#....#.......#....#...............#.#..##..##.........#....#..............#....###...#...
|
||||||
|
...#.......#..##..#..#......................#......##......#........#...#........##.##.#..................#...#.#....##..##......#.
|
||||||
|
...#.......#.........#.........................#...................#......#.......#...#...#.......#............#........###........
|
||||||
|
.#.#.#...#.#........##..................#...#.#.........................#......#.....#..#.#........##............#...........#.....
|
||||||
|
.#.#...#.....###.#........##...........#..#...##.........#...###..#.#...#....##........#...#.............#...#........##...#.....#.
|
||||||
|
..............#..........#...#........#.......##..##........................#................#........##.........#.................
|
||||||
|
....##.................#..................................#.............##..#.#....#...#..#...................#.....#....#.#.#.....
|
||||||
|
....#####...##...#..##..#..#.......###.....#.#......#..#..#.##.....#..#.................#..........................#.#.##.#........
|
||||||
|
..........#..#....##.#.................#......#...#.#.......#......##.........#..#.#.....................................#..#......
|
||||||
|
..##..##.....#.....#....#...........#.#..........#............#.......###....................#..#..........#....#............#...#.
|
||||||
|
......#..........#.......................#...#......#...#...#..#....#..#.....#...........#..#....#............#.....#....#.#.......
|
||||||
|
.#..#......#...#..##................##..#...#.........#.........#.#..#..................#..........................#...#..#.##.....
|
||||||
|
..#......#..#..................................#.....#.###.#.........#......#.#...#................#..........#....#...............
|
||||||
|
........#..##....#...................#........#....#...#..........#...#...#..........####.....#..##.#................#.........###.
|
||||||
|
....#..............................#..#..#..#.##......#...#...................#.##..........#..#...#..................#....###.##..
|
||||||
|
.#..........................#.#..#...........#..#......#..#..#........................#........................##...#.#..#......#..
|
||||||
|
............................#..#...#..................#................#..............##.#.#.#..................#...........##.#...
|
||||||
|
.........#..###............#.....##...#..#...#.##.....##....#.....#.#.......#.#...#........##.........#.#..............#.#.....#...
|
||||||
|
...........#............#.........#.....##...##......#.........#...##...............#.##................#............#.....#...#...
|
||||||
|
.#####.#..#...............................#..#...............#...................#.....#.#............#................#...#.......
|
||||||
|
.#..#...#....#....................#...........#.................................................#......##................#....##.#.
|
||||||
|
....#......#..........#..##...#..#.##....#...#.....#.#........#...#.....#.....#......#...#..#..#..#........................#....#..
|
||||||
|
...#.....#..........##......#..#.....##...#...#...#.#..........#..............#.....#..........#..#.....###.................###....
|
||||||
|
.....................##...#....#....#......#...#.#.......#...........#..........#..............#.......##.................#..#.....
|
||||||
|
..##.................#.......#...........#.##........#..##.#...........#.#....#.#.......#..##....#.#..#....#....#..................
|
||||||
|
.....#...........#.#........#..........#..#.##.....#............#.......#..#.....##....#.#...........##.......#............#.......
|
||||||
|
.....##.#.............##........##...........#..#.#..##.#.......#.......#..................#.#..#..#.......#.................#.#...
|
||||||
|
.#.#..............##....#.......#......#..#........#..................#.#.##..#...#....#.#...........##.....#..#..#.........##.....
|
||||||
|
..............##................#....#....#........#.......#...##...#.#.#........#.#...#...#..#.#.......#.#...#....................
|
||||||
|
.............####.....#..........................#.#..................................#........#.#..##...#...#..#..................
|
||||||
|
.#......................#.....#####.#...........#.#............#.............##....#....#.#...........##..........##...........##..
|
||||||
|
...........#.#.#..#...##...##........#.......#.......#.#........#.......#......#............#..###....#.......#..#.....#........#..
|
||||||
|
............#....#...............#.##............#...##....#.#...........#........#...#...##...........#..........#................
|
||||||
|
......................#............#..##......#......#....#.......#..##......#...#....#....#....#..#..#..........#.....#.#.........
|
||||||
|
................#.....##.......#....##..#.......#......###......#.......#....#.......#....##...........#.#....#....##....#.........
|
||||||
|
................#..#...#.##...#...#....#.........#....#...##......#.#...#....#.............#.....#............##...#...............
|
||||||
|
......................#....#......#.#....##...#...#...#.#.......#.....#..#.......#...#.#.##..#........#.....#....#.........#.......
|
||||||
|
.....##..#..#......................#.#........#....#......#....#..#....#.........#..#.......#.......#.......#.#.......#.###..#.....
|
||||||
|
.................................................................S.................................................................
|
||||||
|
..................#...#.....#....#...........#..#.#..........#............................#....................##.....#....#.......
|
||||||
|
.........#....#......#..#......#...#.#......#...#...#..............#....##.##........#..........##...##...#.......##.#....#........
|
||||||
|
................#.##.#..#..............#.....#..#......#....#............#.#...###..#......#......#....#........#..##..............
|
||||||
|
.........#.....................................#...#.#.............#.....#...........#........###.....................#.#..........
|
||||||
|
.........#....#...........#...##..#........#..........#.#.....#.................#.#.#.##..#...#.#................#....#............
|
||||||
|
...................#...................#...#..............#.....#.#.......#..............#......#..........###.......#..#..........
|
||||||
|
...........#.#.............##...#...#....#.#.....#....................#.....#..#.....#........##.#....#....#...................##..
|
||||||
|
.#................#.#.#.##.............#..#...#....#.#..####.#.......##......................#.......#....#....##................#.
|
||||||
|
...##..............###...#.#..#..#.#...................#....#...#..#.#....##.....#.....#........#...#...#.#.#...................##.
|
||||||
|
................................##.#..........#........#..........#.#....#.........##.......##........#............................
|
||||||
|
...#............##......#.........#.....#.#................##......#.......#....##...#....#.....#.#..#....#.#.....#.............#..
|
||||||
|
......#.........#.....###.##...#..#...#..#.##....#.#.....#.#.#........##...#..#..........#.............#...................#.......
|
||||||
|
.#....#............#.....#..##....##...##.....#.#......##..#........#..........#.................#.......#......#.............#....
|
||||||
|
...#.....#........#......#...........#..#......#.#.#...#....#.###.....##...##..#...#......#..#..........#..#..#..........#.....#...
|
||||||
|
..#.#..#...........#.###...#.......#..........#...#.........#.#....#......#.........#...#....#...#.##....#....#..........##....#...
|
||||||
|
......#.#...#............##.......#.......##...............#..................#.#....#..#..#..#..#...#...#...#.....................
|
||||||
|
....#.......................#........##..#........##.....#.............#........#.#...........#.....#....##...........#..#.........
|
||||||
|
...#.......#..#.......#......#....#......#..........#.#.#.#.......##....#....................##.........#................#..#......
|
||||||
|
..#....................###.......##.#.....#.....#.#............##..#....#..#.................#...#..##.###............#...#..##....
|
||||||
|
.....#......#..#...............#.....##......#.....#.......#..#.#..#....#..##.................##....#....##................#....#..
|
||||||
|
.............##..#.........#..#..#........#..#..........#...#................###..........##.#.#.........#........#....##..#..#....
|
||||||
|
.#.#.#.......#..............#....#...#............#.......#....#.........#........#....#............#............#...#.#..#........
|
||||||
|
.............#.....#.........................#....#.#...........#.................#.#..#....#..........................#.##...#....
|
||||||
|
...#......#........#.............#..................#.###....................#.#.....#........#.....#.........#.#.#.....#.#........
|
||||||
|
.#.............#...##...........#.....#.....#.............#.........#...............###....#...#..#.#............#.#.............#.
|
||||||
|
............##..#................#....#.......#............##.........##..................#......................#.#..#....#.......
|
||||||
|
............#......#.....................#.#.#.#..#.#..#......#.............#.#....##.....#....#...............#.#............#....
|
||||||
|
..#..#.#.#.#....#......#............##..............#....##.........#.......#.....#...##.....#....................#.......#.....#..
|
||||||
|
...#...........#.......#...................#......#...#.##....##....#..#.#...##..#..........#...##............#..#........#.....#..
|
||||||
|
.....#....#..#..##................#...#...#....#.#....#.#.............#...#..............#.##.............#..#..#....#.#...#...#.#.
|
||||||
|
.......#..#.........#.....#..........#......#.#...#.........#.#.....#...#..........#....................#....#..........#..........
|
||||||
|
..#.#.#.....#.........#..###...........#.##.#.......#..#..........#.#.......#......#......#.#.........#.#....#..#..#.......#....#..
|
||||||
|
.#.........#...#......#...............#......#.#.....#.....................#.......#.#......#..................#...............##..
|
||||||
|
..#....#..............................#.....#.##.....#........#....#......#....#....#..#....#........###..#..#..........#....#..#..
|
||||||
|
....#.......##........##..............................#.........#...###.#........#...#.##.............##.....#.#......#..........#.
|
||||||
|
...#.#.##.....#........#.................#...#..#........#............#..#.#........#....................#.....#........#..........
|
||||||
|
.........#....#.........#.......##...........#.#.#.#..............#......#..#.......................#.#......................#.....
|
||||||
|
............#........#..##..#................#..#.............#.............####....#..#.........#............................#....
|
||||||
|
....#......#..##...#...#.#...................#.....#.....#.........#.............#...............#...............###.......#.#.....
|
||||||
|
.#.....#..........................#...........#...............#............##......#.#..........#.......#..........................
|
||||||
|
...##.....................#....#...#.........#...............#..#......##.#...#.#..................#.......#.......................
|
||||||
|
...#........#....#....................#............#.#...#...............#................................##..........##....#.#....
|
||||||
|
.#...##.....#........####....#......#.#......................#.............#..#....#.......#...........#..#.........#..............
|
||||||
|
......#..............#...........#..##.....................#.#.......#.#..###.............#......#.......#..#...#...............#..
|
||||||
|
...#....#...................##...................#.#.#.#...##.....#.#.......#.#..........#............#..............##.......#....
|
||||||
|
...........#.................##.........#..............#.......##..##..#.#................##.#.#..#.#.#.............#..............
|
||||||
|
........#..##.....#.#.......#.........................#....##.........###.....##........#..........#..#...#............#...#....#..
|
||||||
|
...................#.#.#......#..#.........#............#..#........#........#............#....#...........#.......................
|
||||||
|
.......#..........#.............#.#.#..#....#...............#..............#...........##..#...#..................#..........##..#.
|
||||||
|
..............##....#....#..#.....#..........#.........#.#...#.....###..#.............#...................#..#.#.#....##..#....#...
|
||||||
|
...##..........#.....#.#.#...##...#...#........#............#........#.#..............#.....#........#..##...........#.#........#..
|
||||||
|
.#..#.#....#..##.##....##.#....##....#...#...#..........#..##.......#...................#.......##..........#........#...#.#....#..
|
||||||
|
.#..#....#........#......#...............###.............#..........#...#...............#........#...#...###....#..#.#.........#...
|
||||||
|
.....#.........#.#..#....#...#.....#......#.................#...#....#...............#.........#.........#...........#.#...........
|
||||||
|
..##.....#..........#...#..#.....#....#.#.....................#...#.................#.....#..#...#.#................#.........##.#.
|
||||||
|
.........#..#.##........#...####......#.......#................#...#............#..#.#...........#....#.....#.#....#...###.........
|
||||||
|
.........#......#...#...#....#...#.....##..#..##.....#..............#........#........#.........#...........#.....#......#.#..#....
|
||||||
|
...##.......#.....#....#.............#.##...#.#....................................#.#...#...............#...................#.....
|
||||||
|
......................#.###.............#........#.................................#.##........#..#.#.............##...#...........
|
||||||
|
...#........#....#.....#.#...........#.#.......#....#.............#................#.....#..#..#..#.#.......#...#.....#.....##.....
|
||||||
|
.##.#....#.........#........##......#................##............................#...#..................#...##............##.....
|
||||||
|
......#.......#........#..#.#...#.........#............#.#........................#..#....#.#...##.........#...#..........##.......
|
||||||
|
............#.#...#.....#..#..........#.....#..........................###.#.......##..#......#...#......#.........##...###.....#..
|
||||||
|
.#.#......#.#..............#............#..........#.#....................#......#..#...#....#..#.#......#...............#.#.......
|
||||||
|
...................................................................................................................................
|
||||||
11
inputs/21a.txt
Normal file
11
inputs/21a.txt
Normal file
@ -0,0 +1,11 @@
|
|||||||
|
...........
|
||||||
|
.....###.#.
|
||||||
|
.###.##..#.
|
||||||
|
..#.#...#..
|
||||||
|
....#.#....
|
||||||
|
.##..S####.
|
||||||
|
.##..#...#.
|
||||||
|
.......##..
|
||||||
|
.##.#.####.
|
||||||
|
.##..##.##.
|
||||||
|
...........
|
||||||
133
src/21.cs
Normal file
133
src/21.cs
Normal file
@ -0,0 +1,133 @@
|
|||||||
|
using aoc2023.Util;
|
||||||
|
|
||||||
|
namespace aoc2023;
|
||||||
|
|
||||||
|
internal class Day21 : Day
|
||||||
|
{
|
||||||
|
private int width;
|
||||||
|
private int height;
|
||||||
|
private readonly HashSet<ivec2> garden = [];
|
||||||
|
private ivec2 start = new(0, 0);
|
||||||
|
|
||||||
|
internal override void Parse()
|
||||||
|
{
|
||||||
|
var lines = Parsing.ReadAllLines($"{GetDay()}").ToList();
|
||||||
|
height = lines.Count;
|
||||||
|
for (int y = 0; y < height; y++)
|
||||||
|
{
|
||||||
|
width = lines[y].Length;
|
||||||
|
for (int x = 0; x < width; x++)
|
||||||
|
{
|
||||||
|
if (lines[y][x] == '.' || lines[y][x] == 'S')
|
||||||
|
{
|
||||||
|
var pt = new ivec2(x, y);
|
||||||
|
garden.Add(pt);
|
||||||
|
|
||||||
|
if (lines[y][x] == 'S')
|
||||||
|
{
|
||||||
|
start = pt;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
private long FillGrid(long startY, long startX, long steps)
|
||||||
|
{
|
||||||
|
HashSet<(long, long)> filled = [];
|
||||||
|
HashSet<(long, long)> visited = [];
|
||||||
|
Queue<(long y, long x, long step)> q = [];
|
||||||
|
q.Enqueue((startY, startX, steps));
|
||||||
|
|
||||||
|
while (q.TryDequeue(out (long y, long x, long step) currLoc))
|
||||||
|
{
|
||||||
|
if (currLoc.step % 2 == 0)
|
||||||
|
{
|
||||||
|
filled.Add((currLoc.y, currLoc.x));
|
||||||
|
}
|
||||||
|
|
||||||
|
if (currLoc.step == 0)
|
||||||
|
{
|
||||||
|
continue;
|
||||||
|
}
|
||||||
|
|
||||||
|
foreach (var (newY, newX) in ((long, long c)[]) [(currLoc.y + 1, c: currLoc.x), (currLoc.y - 1, c: currLoc.x), (currLoc.y, currLoc.x + 1), (currLoc.y, currLoc.x - 1)])
|
||||||
|
{
|
||||||
|
if (newY < 0 || newY >= height || newX < 0 || newX >= width || !garden.Contains(new ivec2(newY, newX)) ||
|
||||||
|
!visited.Add((newY, newX)))
|
||||||
|
{
|
||||||
|
continue;
|
||||||
|
}
|
||||||
|
|
||||||
|
q.Enqueue((newY, newX, currLoc.step - 1));
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
return filled.Count;
|
||||||
|
}
|
||||||
|
|
||||||
|
internal override string Part1()
|
||||||
|
{
|
||||||
|
HashSet<ivec2> next = [start];
|
||||||
|
HashSet<ivec2> reachableNow = [];
|
||||||
|
const int numSteps = 64;
|
||||||
|
for (int step = 0; step < numSteps; step++)
|
||||||
|
{
|
||||||
|
HashSet<ivec2> curr = [..next];
|
||||||
|
next.Clear();
|
||||||
|
foreach (var pos in curr)
|
||||||
|
{
|
||||||
|
foreach (var neighbor in pos.GetBoundedOrthogonalNeighbors(0, 0, width, height))
|
||||||
|
{
|
||||||
|
if (!garden.Contains(neighbor))
|
||||||
|
{
|
||||||
|
continue;
|
||||||
|
}
|
||||||
|
|
||||||
|
if (step == numSteps - 1)
|
||||||
|
{
|
||||||
|
reachableNow.Add(neighbor);
|
||||||
|
}
|
||||||
|
|
||||||
|
next.Add(neighbor);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
long numVisited = reachableNow.Count;
|
||||||
|
return $"<+white>{numVisited}";
|
||||||
|
}
|
||||||
|
|
||||||
|
internal override string Part2()
|
||||||
|
{
|
||||||
|
const long steps = 26501365;
|
||||||
|
long gridWidth = steps / width - 1;
|
||||||
|
long odd = (long)System.Math.Pow(gridWidth / 2 * 2 + 1, 2);
|
||||||
|
long even = (long)System.Math.Pow((gridWidth + 1) / 2 * 2, 2);
|
||||||
|
|
||||||
|
long oddPoints = FillGrid(start.y, start.x, width * 2 + 1);
|
||||||
|
long eventPoints = FillGrid(start.y, start.x, width * 2);
|
||||||
|
|
||||||
|
long cornerTop = FillGrid(width - 1, start.x, width - 1);
|
||||||
|
long cornerRight = FillGrid(start.y, 0, width - 1);
|
||||||
|
long cornerBottom = FillGrid(0, start.x, width - 1);
|
||||||
|
long cornerLeft = FillGrid(start.y, width - 1, width - 1);
|
||||||
|
|
||||||
|
long smallTopRight = FillGrid(width - 1, 0, width / 2 - 1);
|
||||||
|
long smallTopLeft = FillGrid(width - 1, width - 1, width / 2 - 1);
|
||||||
|
long smallBottomRight = FillGrid(0, 0, width / 2 - 1);
|
||||||
|
long smallBottomLeft = FillGrid(0, width - 1, width / 2 - 1);
|
||||||
|
|
||||||
|
long largeTopRight = FillGrid(width - 1, 0, width * 3 / 2 - 1);
|
||||||
|
long largeTopLeft = FillGrid(width - 1, width - 1, width * 3 / 2 - 1);
|
||||||
|
long largeBottomRight = FillGrid(0, 0, width * 3 / 2 - 1);
|
||||||
|
long largeBottomLeft = FillGrid(0, width - 1, width * 3 / 2 - 1);
|
||||||
|
|
||||||
|
long numVisited = odd * oddPoints +
|
||||||
|
even * eventPoints +
|
||||||
|
cornerTop + cornerRight + cornerBottom + cornerLeft +
|
||||||
|
(gridWidth + 1) * (smallTopRight + smallTopLeft + smallBottomRight + smallBottomLeft) +
|
||||||
|
gridWidth * (largeTopRight + largeTopLeft + largeBottomRight + largeBottomLeft);
|
||||||
|
return $"<+white>{numVisited}";
|
||||||
|
}
|
||||||
|
}
|
||||||
Reference in New Issue
Block a user