Day 5

src/main/kotlin/com/basdado/adventofcode/Day5.kt

@@ -0,0 +1,126 @@
+package com.basdado.adventofcode
+
+import kotlin.math.abs
+import kotlin.system.measureTimeMillis
+
+fun main() {
+
+    val day = Day5()
+    println("Puzzle 1 time: " + measureTimeMillis { day.puzzle1() } + " ms")
+    println("Puzzle 2 time: " + measureTimeMillis { day.puzzle2() } + " ms")
+
+}
+
+class Day5 {
+
+    fun puzzle1() {
+
+        val polymer = constructPolymerFromString(lines("/day/5/input.txt").findFirst().get())
+        polymer.react()
+        println(polymer.length())
+    }
+
+    fun puzzle2() {
+
+        val fullPolymerString = lines("/day/5/input.txt").findFirst().get()
+        println(fullPolymerString.chars()
+            .distinct().boxed()
+            .map { it.toChar() }.map { it.toString() }
+            .map { it.toUpperCase() }
+            .distinct()
+            .mapToInt { constructPolymerFromString(fullPolymerString.replace(it.toString(), "", true)).react().length() }
+            .min()!!
+        )
+    }
+
+    fun constructPolymerFromString(str: String): Polymer {
+
+        val polymer = Polymer()
+        if (!str.isBlank()) {
+
+            polymer.firstUnit = Unit(str[0])
+
+            var previousUnit = polymer.firstUnit!!
+            for (i in 1 until str.length) {
+                val newUnit = Unit(str[i], previous = previousUnit)
+                previousUnit.next = newUnit
+                previousUnit = newUnit
+            }
+        }
+        return polymer
+    }
+
+    class Polymer (var firstUnit: Unit? = null) {
+
+        fun react(): Polymer {
+
+            if (firstUnit == null) {
+                return this
+            }
+
+            var curUnit = firstUnit!!
+            do {
+                if (curUnit.reactsWithNext()) {
+                    if (curUnit.previous == null) {
+                        // This is the first unit in the chain, so we update the polymer
+                        firstUnit = curUnit.next?.next
+                        if (firstUnit == null) {
+                            break
+                        }
+                        firstUnit!!.previous = null
+                        curUnit = firstUnit!!
+                    } else {
+                        val nextAfterReaction = curUnit.next?.next
+                        curUnit = curUnit.previous!! // one step back
+                        nextAfterReaction?.previous = curUnit
+                        curUnit.next = nextAfterReaction
+                    }
+                } else {
+                    curUnit = curUnit.next!!
+                }
+            } while(curUnit.hasNext())
+            return this
+        }
+
+        fun length(): Int {
+            if (firstUnit == null) {
+                return 0
+            }
+            var curUnit = firstUnit!!
+            var length = 0
+            do {
+                length++
+                curUnit = curUnit.next!!
+            } while(curUnit.hasNext())
+            // Don't forget to count the last character
+            length++
+            return length
+        }
+
+        override fun toString(): String {
+            if (firstUnit == null) {
+                return ""
+            }
+
+            val res = StringBuilder()
+            var curUnit = firstUnit!!
+            do {
+                res.append(curUnit.char)
+                curUnit = curUnit.next!!
+            } while (curUnit.hasNext())
+            res.append(curUnit.char)
+            return res.toString()
+        }
+    }
+
+    data class Unit (val char: Char, var next: Unit? = null, var previous: Unit? = null) {
+        fun reactsWithNext(): Boolean  = reactsWith(next)
+        fun reactsWithPrevious(): Boolean  = reactsWith(previous)
+        fun reactsWith(unit: Unit?): Boolean = if (unit == null) false else abs(char.minus(unit.char)) == 32
+        fun hasNext(): Boolean = next != null
+        fun hasPrevious(): Boolean = previous != null
+        override fun toString(): String {
+            return "" + char
+        }
+    }
+}