Day 18

day18/part1.kts

@@ -0,0 +1,62 @@
+#!/usr/bin/env kotlin
+
+import java.io.File
+import java.util.LinkedList
+
+data class Block (
+    var type: Type,
+    var seen: Boolean = false,
+    var distance: Int = Int.MAX_VALUE
+) {
+    enum class Type {
+        Empty,
+        Byte,
+    }
+}
+
+val bytes = File("input.txt").readLines().subList(0, 1024).map { it.split(",").let { s -> s[0].toInt() to s[1].toInt() } }.toSet()
+val grid = (0..70).map { row -> (0..70).map { col ->
+    Block(
+        type = if (bytes.contains(col to row)) Block.Type.Byte
+               else Block.Type.Empty,
+    )
+}.toMutableList() }.toMutableList()
+grid[0][0].seen = true
+grid[0][0].distance = 0
+
+val queue = LinkedList<Pair<Int, Int>>()
+queue.addFirst(0 to 0)
+
+while (!queue.isEmpty()) {
+    // Take one off the queue
+    val next = queue.pollLast() ?: break
+
+    // Check if we reached goal
+    if (next.first == 70 && next.second == 70) {
+        break
+    }
+
+    // Add neighbors
+    if ((0..70).contains(next.first + 1) && grid[next.first + 1][next.second].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+        grid[next.first + 1][next.second].seen = true
+        grid[next.first + 1][next.second].distance = grid[next.first][next.second].distance + 1
+        queue.addFirst(next.first + 1 to next.second)
+    }
+    if ((0..70).contains(next.second + 1) && grid[next.first][next.second + 1].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+        grid[next.first][next.second + 1].seen = true
+        grid[next.first][next.second + 1].distance = grid[next.first][next.second].distance + 1
+        queue.addFirst(next.first to next.second + 1)
+    }
+    if ((0..70).contains(next.first - 1) && grid[next.first - 1][next.second].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+        grid[next.first - 1][next.second].seen = true
+        grid[next.first - 1][next.second].distance = grid[next.first][next.second].distance + 1
+        queue.addFirst(next.first - 1 to next.second)
+    }
+    if ((0..70).contains(next.second - 1) && grid[next.first][next.second - 1].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+        grid[next.first][next.second - 1].seen = true
+        grid[next.first][next.second - 1].distance = grid[next.first][next.second].distance + 1
+        queue.addFirst(next.first to next.second - 1)
+    }
+}
+
+println(grid[70][70].distance)

day18/part2.kts

@@ -0,0 +1,70 @@
+#!/usr/bin/env kotlin
+
+import java.io.File
+import java.util.LinkedList
+
+data class Block (
+    var type: Type,
+    var seen: Boolean = false,
+    var distance: Int = Int.MAX_VALUE
+) {
+    enum class Type {
+        Empty,
+        Byte,
+    }
+}
+
+var cutOff = -1
+for (byteCount in 1025..File("input.txt").readLines().count()) {
+    val bytes = File("input.txt").readLines().subList(0, byteCount).map { it.split(",").let { s -> s[0].toInt() to s[1].toInt() } }.toSet()
+    val grid = (0..70).map { row -> (0..70).map { col ->
+        Block(
+            type = if (bytes.contains(col to row)) Block.Type.Byte
+            else Block.Type.Empty,
+        )
+    }.toMutableList() }.toMutableList()
+    grid[0][0].seen = true
+    grid[0][0].distance = 0
+
+    val queue = LinkedList<Pair<Int, Int>>()
+    queue.addFirst(0 to 0)
+
+    while (!queue.isEmpty()) {
+        // Take one off the queue
+        val next = queue.pollLast() ?: break
+
+        // Check if we reached goal
+        if (next.first == 70 && next.second == 70) {
+            break
+        }
+
+        // Add neighbors
+        if ((0..70).contains(next.first + 1) && grid[next.first + 1][next.second].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+            grid[next.first + 1][next.second].seen = true
+            grid[next.first + 1][next.second].distance = grid[next.first][next.second].distance + 1
+            queue.addFirst(next.first + 1 to next.second)
+        }
+        if ((0..70).contains(next.second + 1) && grid[next.first][next.second + 1].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+            grid[next.first][next.second + 1].seen = true
+            grid[next.first][next.second + 1].distance = grid[next.first][next.second].distance + 1
+            queue.addFirst(next.first to next.second + 1)
+        }
+        if ((0..70).contains(next.first - 1) && grid[next.first - 1][next.second].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+            grid[next.first - 1][next.second].seen = true
+            grid[next.first - 1][next.second].distance = grid[next.first][next.second].distance + 1
+            queue.addFirst(next.first - 1 to next.second)
+        }
+        if ((0..70).contains(next.second - 1) && grid[next.first][next.second - 1].let { it.type == Block.Type.Empty && it.distance > grid[next.first][next.second].distance + 1 }) {
+            grid[next.first][next.second - 1].seen = true
+            grid[next.first][next.second - 1].distance = grid[next.first][next.second].distance + 1
+            queue.addFirst(next.first to next.second - 1)
+        }
+    }
+
+    if (grid[70][70].distance == Int.MAX_VALUE) {
+        cutOff = byteCount
+        break
+    }
+}
+
+println(File("input.txt").readLines()[cutOff - 1])