commit 82ebf9678c26287d141b8e57b558d33a3cda294b
parent 6fbdad0ba52401ad8b286099882b60ab07701dec
Author: Luís Ferreira <contact@lsferreira.net>
Date: Fri, 17 Dec 2021 23:18:42 +0000
posts: Add 'Solution in D for Advent of Code 2021, Day 5'
Signed-off-by: Luís Ferreira <contact@lsferreira.net>
Diffstat:
1 file changed, 87 insertions(+), 0 deletions(-)
diff --git a/content/posts/zet-6-aoc-2021-05.md b/content/posts/zet-6-aoc-2021-05.md
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+---
+title: 'Zettelkasten #6: Solution in D for Advent of Code 2021, Day 5'
+date: '2021-12-17T22:11:00+01:00'
+tags: ['zettelkasten', 'zet', 'dlang', 'aoc', 'aoc2021', 'adventofcode']
+description: "This post describes my solution in the D programming language for
+the 5th puzzle of the Advent of Code 2021."
+---
+
+## The challenge
+
+### Part 1
+
+> You come across a field of hydrothermal vents on the ocean floor! These vents
+> constantly produce large, opaque clouds, so it would be best to avoid them if
+> possible.
+>
+> They tend to form in lines; the submarine helpfully produces a list of nearby
+> lines of vents (your puzzle input) for you to review.
+>
+> [...]
+>
+> Each line of vents is given as a line segment in the format x1,y1 -> x2,y2
+> where x1,y1 are the coordinates of one end the line segment and x2,y2 are the
+> coordinates of the other end. These line segments include the points at both
+> ends. In other words:
+>
+> - An entry like 1,1 -> 1,3 covers points 1,1, 1,2, and 1,3.
+> - An entry like 9,7 -> 7,7 covers points 9,7, 8,7, and 7,7.
+>
+> For now, only consider horizontal and vertical lines: lines where either x1 =
+> x2 or y1 = y2.
+>
+> [...]
+>
+> To avoid the most dangerous areas, you need to determine the number of points
+> where at least two lines overlap. [...]
+>
+> Consider only horizontal and vertical lines. At how many points do at least
+> two lines overlap?
+
+You can read the challenge more in depth,
+[here](https://adventofcode.com/2021/day/5).
+
+### Part 2
+
+> Unfortunately, considering only horizontal and vertical lines doesn't give
+> you the full picture; you need to also consider diagonal lines.
+>
+> Because of the limits of the hydrothermal vent mapping system, the lines in
+> your list will only ever be horizontal, vertical, or a diagonal line at
+> exactly 45 degrees. In other words:
+>
+> - An entry like 1,1 -> 3,3 covers points 1,1, 2,2, and 3,3.
+> - An entry like 9,7 -> 7,9 covers points 9,7, 8,8, and 7,9.
+>
+> [...]
+>
+> Consider all of the lines. At how many points do at least two lines overlap?
+
+## Full solution
+
+```d
+auto input = stdin.byLineCopy()
+ .map!`a.splitter(" -> ").map!"a.splitter(',').map!(to!long).array".array`.array;
+auto xy =input.map!(l => [max(l[0][0], l[1][0]), max(l[0][1],l[1][1])])
+ .array.transposed.map!maxElement.array;
+size_t[][] a = new size_t[(xy[0]+1)*(xy[1]+1)].evenChunks(xy[1]+1).array;
+foreach(p; input) {
+ if(p[0][0] == p[1][0])
+ if(p[0][1] > p[1][1]) foreach(e; p[1][1]..p[0][1]+1) ++a[e][p[0][0]];
+ else foreach(e; p[0][1]..p[1][1]+1) ++a[e][p[0][0]];
+ else if(p[0][1] == p[1][1])
+ if(p[1][0] > p[0][0]) foreach(e; p[0][0]..p[1][0]+1) ++a[p[0][1]][e];
+ else foreach(e; p[1][0]..p[0][0]+1) ++a[p[0][1]][e];
+ else if(1) // change this value to 0 for first part
+ {
+ auto x1 = p[0][0], x2 = p[1][0], y1 = p[0][1], y2 = p[1][1];
+ if(x1 > x2) { swap(x1,x2); swap(y1, y2); }
+ foreach(e; x1..x2+1)
+ if(y2>y1) ++a[y1+(e-x1)][e];
+ else ++a[y1-(e-x1)][e];
+ }
+}
+// construct the map
+//a.map!(l => l.map!`a.to!string == "0" ? "." : a.to!string`.join).each!writeln;
+a.join.filter!"a > 1".count.writeln;
+```
