Day 10 part 1

source/app.d

@@ -17,6 +17,7 @@ import day6;
 import day7;
 import day8;
 import day9;
+import day10;
 import dayutil;
 
 immutable string progName = "aoc-2020";
@@ -35,6 +36,7 @@ Variant function(int, File, bool, string[])[] programs = [
 	&day7.run,
 	&day8.run,
 	&day9.run,
+	&day10.run,
 ];
 
 void printUsage(string message = null) {

source/day10.d

@@ -0,0 +1,38 @@
+import std.array;
+import std.algorithm;
+import std.conv;
+import std.range;
+import std.stdio;
+import std.variant;
+
+import dayutil;
+
+Variant run(int part, File input, bool bigboy, string[] args) {
+	uint[] numbers = input.byLineCopy.map!(to!uint).array ~ [0u];
+	auto sortedNumbers = numbers.sort;
+
+	Variant result = parts!size_t(part,
+			() => part1(sortedNumbers));
+	return result;
+}
+
+size_t part1(T)(SortedRange!(T[]) numbers) {
+	size_t gap1 = 0, gap3 = 0;
+
+	foreach(window; numbers.slide!(No.withPartial)(2)) {
+		size_t diff = window[1] - window[0];
+		if (diff == 3) gap3++;
+		if (diff == 1) gap1++;
+	}
+	// Device adapter is always rated 3 volts higher
+	gap3++;
+	writeln(gap1, ", ", gap3);
+	return gap1 * gap3;
+}
+
+unittest {
+	uint[] numbers = [28, 33, 18, 42, 31, 14, 46, 20, 48, 47, 24, 23, 49, 45, 19, 38, 39, 11, 1, 32, 
+		 25, 35, 8, 17, 7, 9, 4, 2, 34, 10, 3];
+	numbers ~= [0u];
+	assert(part1(numbers.sort) == 220);
+}