diff --git a/src/Utils.kt b/src/Utils.kt
index 7ff1419..b158c9f 100644
--- a/src/Utils.kt
+++ b/src/Utils.kt
@@ -1,12 +1,6 @@
+import java.io.File
 import java.math.BigInteger
 import java.security.MessageDigest
-import kotlin.io.path.Path
-import kotlin.io.path.readText
-
-/**
- * Reads lines from the given input txt file.
- */
-fun readInput(name: String) = Path("src/$name.txt").readText().trim().lines()
 
 /**
  * Converts string to md5 hash.
@@ -19,3 +13,37 @@ fun String.md5() = BigInteger(1, MessageDigest.getInstance("MD5").digest(toByteA
  * The cleaner shorthand for printing output.
  */
 fun Any?.println() = println(this)
+
+private fun openFile(day: Int, name: String) = File("inputs/day%02d".format(day), "$name.txt")
+
+/**
+ * Reads lines from the given input txt file.
+ */
+fun readInput(day: Int, name: String) = openFile(day, name).readText().trim().lines()
+
+fun readInputAsString(day: Int, name: String) = openFile(day, name).readText()
+fun readInputAsInts(day: Int, name: String) = readInput(day, name).map { it.toInt() }
+fun readInputAsCommaSeparatedInts(day: Int, name: String) = openFile(day, name)
+    .readText()
+    .split(",")
+    .map { it.toInt() }
+
+fun readGraph(day: Int, name: String) = readInput(day, name).fold(mapOf<String, Set<String>>()) { currentGraph, edge ->
+    val (fromVertex, toVertex) = edge.split("-")
+    val fromNeighbours = currentGraph.getOrDefault(fromVertex, emptySet()) + toVertex
+    val toNeighbours = currentGraph.getOrDefault(toVertex, emptySet()) + fromVertex
+
+    currentGraph + mapOf(fromVertex to fromNeighbours, toVertex to toNeighbours)
+}.toMap()
+
+fun <A, B> product(xs: Sequence<A>, ys: Sequence<B>): Sequence<Pair<A, B>> =
+    xs.flatMap { x -> ys.map { y -> x to y } }
+
+fun <A, B, C> product(xs: Sequence<A>, ys: Sequence<B>, zs: Sequence<C>): Sequence<Triple<A, B, C>> =
+    xs.flatMap { x -> ys.flatMap { y -> zs.map { z -> Triple(x, y, z) } } }
+
+fun <A, B> product(xs: Iterable<A>, ys: Iterable<B>): Sequence<Pair<A, B>> =
+    product(xs.asSequence(), ys.asSequence())
+
+fun <A, B, C> product(xs: Iterable<A>, ys: Iterable<B>, zs: Iterable<C>): Sequence<Triple<A, B, C>> =
+    product(xs.asSequence(), ys.asSequence(), zs.asSequence())