From 52629702c8ae1166e235b9fadfa9d62816151d70 Mon Sep 17 00:00:00 2001
From: Henk Kalkwater <chris@netsoj.nl>
Date: Thu, 3 Dec 2020 10:50:55 +0100
Subject: [PATCH] Day 3, part 1

---
 source/app.d  |  4 +++-
 source/day3.d | 31 +++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 source/day3.d

diff --git a/source/app.d b/source/app.d
index f86d5d9..f5e3c24 100644
--- a/source/app.d
+++ b/source/app.d
@@ -7,13 +7,15 @@ import std.getopt;
 
 import day1;
 import day2;
+import day3;
 import dayutil;
 
 immutable string progName = "aoc-2020";
 
 void function(string[])[] programs = [
 	&day1.run,
-	&day2.run
+	&day2.run,
+	&day3.run,
 ];
 
 void printUsage(string name) {
diff --git a/source/day3.d b/source/day3.d
new file mode 100644
index 0000000..f180c29
--- /dev/null
+++ b/source/day3.d
@@ -0,0 +1,31 @@
+import std.algorithm;
+import std.format;
+import std.range;
+import std.stdio;
+import std.uni;
+
+void run(string[] args) {
+	ulong count = stdin.byLine.countTrees;
+	writeln(count);
+}
+
+ulong countTrees(Range)(Range lines) if (isInputRange!Range) {
+	return lines.enumerate.filter!(x => (x.value[x.index * 3 % x.value.length] == '#')).count;
+}
+
+unittest {
+	string[] field = [
+		"..##.........##.........##.........##.........##.........##.......",
+		"#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..",
+		".#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.",
+		"..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#",
+		".#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.",
+		"..#.##.......#.##.......#.##.......#.##.......#.##.......#.##.....",
+		".#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#",
+		".#........#.#........#.#........#.#........#.#........#.#........#",
+		"#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...",
+		"#...##....##...##....##...##....##...##....##...##....##...##....#",
+		".#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#"
+	];
+	assert(field.countTrees == 7);
+}