Added day 1

.gitignore

@@ -0,0 +1,15 @@
+.dub
+docs.json
+__dummy.html
+docs/
+/aoc-2020
+aoc-2020.so
+aoc-2020.dylib
+aoc-2020.dll
+aoc-2020.a
+aoc-2020.lib
+aoc-2020-test-*
+*.exe
+*.o
+*.obj
+*.lst

in/1.txt

@@ -0,0 +1,200 @@
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source/app.d

@@ -1,6 +1,37 @@
-import std.stdio;
+import core.stdc.stdlib;
+
+import std.conv;
+import std.format;
+import std.stdio;
+import std.getopt;
+
+import day1;
+
+immutable string progName = "aoc-2020";
+
+void function(string[])[] programs = [
+	&day1.run
+];
+
+void main(string[] args) {
+	int day;
+	if (args.length < 2) {
+		stderr.writeln("USAGE: %s [day]".format(args[0]));
+		exit(-1);
+	}
+	try {
+		day = to!int(args[1]);
+	} catch (ConvException e) {
+		stderr.writeln("[day] is not an integer");
+		exit(-1);
+	}
+
+	if (day <= 0 || day > programs.length) {
+		stderr.writeln("Day must be between 1 and %d".format(programs.length - 1));
+		exit(-1);
+	}
+
+	
+	programs[day - 1](args[2..$]);
 
-void main()
-{
-	writeln("Edit source/app.d to start your project.");
 }

source/day1.d

@@ -0,0 +1,58 @@
+import std.algorithm;
+import std.array;
+import std.conv;
+import std.exception;
+import std.format;
+import std.range;
+import std.stdio;
+
+immutable string progName = "aoc-2020";
+
+void run(string[] args) {
+	enforce(args.length == 1, "Please provide a part to run %s 1 [part]".format(progName));
+	int part = to!int(args[0]);
+	enforce(part > 0 &&  part <= 2, "Parts %d to %d supported".format(1, 2));
+
+	auto numbers = stdin.byLineCopy.map!(a => to!int(a)).array.sort;
+
+	auto fun = part == 1 ? &part1 : &part2;
+	writeln(fun(numbers));
+}
+
+int part1(SortedRange!(int[]) numbers) {
+	int result = -1;
+
+	foreach (ref int a; numbers) {
+		int b = 2020 - a;
+		if (numbers.contains(b)) {
+			result = b * a;
+			break;
+		}
+	}
+	return result;
+}
+
+unittest {
+	auto numbers = [1721, 979, 366, 299, 675, 1456].sort;
+	assert(part1(numbers) == 514579);
+}
+
+int part2(SortedRange!(int[]) numbers) {
+	int result = -1;
+	foreach (ref int a; numbers) {
+		foreach (ref int b; numbers) {
+			int c = 2020 - b - a;
+			if (numbers.contains(c)) {
+				result = c * b * a;
+				goto exit;
+			}
+		}
+	}
+exit:
+	return result;
+}
+
+unittest {
+	auto numbers = [1721, 979, 366, 299, 675, 1456].sort;
+	assert(part2(numbers) == 241861950);
+}