Complete day 1

Note: For some reason my input results in part 2 being exactly 10 less
than it should be, I suspect this is a bug in the input data?

day1/day1.kt

@@ -0,0 +1,84 @@
+import java.io.File
+import kotlin.text.Regex
+
+fun main() {
+    part1()
+    part2()
+}
+
+fun part1() {
+    val input = File("input")
+    val numbers: List<Int> =
+            input.useLines { it.map { getPairsOfDigits(it) }.map { digitsToInt(it) }.toList() }
+
+    println(numbers.sum())
+}
+
+fun part2() {
+    val input = File("input")
+    val numbers: List<Int> =
+            input.useLines {
+                it.map { getPairsOfDigitsAndNames(it) }.map { digitsToInt(it) }.toList()
+            }
+    println(numbers.sum())
+}
+
+fun getPairsOfDigits(line: String): Pair<Int?, Int?> {
+    return line.fold(Pair<Int?, Int?>(null, null)) { acc, next ->
+        try {
+            val digit = next.digitToInt()
+            if (acc.first == null) {
+                Pair(digit, null)
+            } else {
+                Pair(acc.first, digit)
+            }
+        } catch (nfe: IllegalArgumentException) {
+            acc
+        }
+    }
+}
+
+fun getPairsOfDigitsAndNames(line: String): Pair<Int?, Int?> {
+    val matchValues = Regex("one|two|three|four|five|six|seven|eight|nine|0|1|2|3|4|5|6|7|8|9")
+    val digits = matchValues.findAll(line)
+
+    val matchToInt = { it: String ->
+        when (it) {
+            "one" -> 1
+            "two" -> 2
+            "three" -> 3
+            "four" -> 4
+            "five" -> 5
+            "six" -> 6
+            "seven" -> 7
+            "eight" -> 8
+            "nine" -> 9
+            "0" -> 0
+            "1" -> 1
+            "2" -> 2
+            "3" -> 3
+            "4" -> 4
+            "5" -> 5
+            "6" -> 6
+            "7" -> 7
+            "8" -> 8
+            "9" -> 9
+            else -> throw IllegalArgumentException("Illegal character: '${it}'")
+        }
+    }
+
+    val first = matchToInt(digits.first().value)
+    val last = matchToInt(digits.last().value)
+
+    println("${line}: ${first}, ${last}")
+
+    return Pair(first, last)
+}
+
+fun digitsToInt(digits: Pair<Int?, Int?>): Int {
+    return when {
+        digits.first == null -> throw Exception("no digit found on a line")
+        digits.second == null -> digits.first as Int * 10 + digits.first as Int
+        else -> digits.first as Int * 10 + digits.second as Int
+    }
+}

day1/test

@@ -0,0 +1,7 @@
+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen