day(02): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

src/Day02.kt

@@ -0,0 +1,60 @@
+enum class Command {
+    FORWARD, DOWN, UP
+}
+
+fun main() {
+    data class Position(val horizontal: Int = 0, val depth: Int = 0, val aim: Int = 0)
+    data class Instruction(val type: Command, val value: Int)
+
+    fun parseInstruction(instruction: String): Instruction {
+        val splitLine = instruction.split(' ')
+        check(splitLine.size == 2)
+
+        val value = splitLine[1].toInt()
+        when (splitLine[0]) {
+            "forward" -> return Instruction(Command.FORWARD, value)
+            "down" -> return Instruction(Command.DOWN, value)
+            "up" -> return Instruction(Command.UP, value)
+        }
+        throw IllegalArgumentException("Cannot parse instruction")
+    }
+
+    fun toCommands(input: List<String>): List<Instruction> {
+        return input.map { parseInstruction(it) }
+    }
+
+    fun part1(input: List<Instruction>): Int {
+        val finalPosition = input.fold(Position()) { pos, instruction ->
+            when (instruction.type) {
+                Command.FORWARD -> pos.copy(horizontal = pos.horizontal + instruction.value)
+                Command.UP -> pos.copy(depth = pos.depth - instruction.value)
+                Command.DOWN -> pos.copy(depth = pos.depth + instruction.value)
+            }
+        }
+        return finalPosition.horizontal * finalPosition.depth
+    }
+
+    fun part2(input: List<Instruction>): Int {
+        val finalPosition = input.fold(Position()) { pos, instruction ->
+            when (instruction.type) {
+                Command.FORWARD -> pos.copy(
+                    horizontal = pos.horizontal + instruction.value,
+                    depth = pos.depth + instruction.value * pos.aim
+                )
+                Command.UP -> pos.copy(aim = pos.aim - instruction.value)
+                Command.DOWN -> pos.copy(aim = pos.aim + instruction.value)
+            }
+        }
+        return finalPosition.horizontal * finalPosition.depth
+    }
+
+
+    val testInput = toCommands(readInput("Day02_test"))
+    val input = toCommands(readInput("Day02"))
+
+    check(part1(testInput) == 150)
+    println(part1(input))
+
+    check(part2(testInput) == 900)
+    println(part2(input))
+}

src/Day02_test.txt

@@ -0,0 +1,6 @@
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2