Day 8

day8/part1.kts

@@ -0,0 +1,52 @@
+#!/usr/bin/env kotlin
+
+import java.io.File
+
+val frequencies = mutableMapOf<Char, MutableList<Pair<Int, Int>>>()
+var gridWidth = 0
+var gridHeight = 0
+File("./input.txt").readLines().also {
+    gridHeight = it.size
+}.forEachIndexed { i, line ->
+    line.also { gridWidth = it.length }.forEachIndexed chars@{ j, freq ->
+        if (freq == '.') return@chars
+        val curValue = frequencies.putIfAbsent(
+            freq, mutableListOf(Pair(i, j))
+        )
+        if (curValue !== null) {
+            curValue.add(Pair(i, j))
+        }
+    }
+}
+
+val antiNodes = hashSetOf<Pair<Int, Int>>()
+frequencies.forEach { (_, points) ->
+    points.forEach outer@{ point1 ->
+        points.forEach { point2 ->
+            if (point1 == point2) return@outer
+            val dRow = (point1.first - point2.first)
+            val dCol = (point1.second - point2.second)
+
+            val antiNode1 = Pair(point1.first + dRow, point1.second + dCol)
+            val antiNode2 = Pair(point2.first - dRow, point2.second - dCol)
+
+            if (
+                antiNode1.first >= 0
+                && antiNode1.second >= 0
+                && antiNode1.first < gridHeight
+                && antiNode1.second < gridWidth) {
+                antiNodes.add(antiNode1)
+            }
+
+            if (
+                antiNode2.first >= 0
+                && antiNode2.second >= 0
+                && antiNode2.first < gridHeight
+                && antiNode2.second < gridWidth) {
+                antiNodes.add(antiNode2)
+            }
+        }
+    }
+}
+
+println(antiNodes.size)

day8/part2.kts

@@ -0,0 +1,49 @@
+#!/usr/bin/env kotlin
+
+import java.io.File
+
+val frequencies = mutableMapOf<Char, MutableList<Pair<Int, Int>>>()
+var gridWidth = 0
+var gridHeight = 0
+File("./input.txt").readLines().also {
+    gridHeight = it.size
+}.forEachIndexed { i, line ->
+    line.also { gridWidth = it.length }.forEachIndexed chars@{ j, freq ->
+        if (freq == '.') return@chars
+        val curValue = frequencies.putIfAbsent(
+            freq, mutableListOf(Pair(i, j))
+        )
+        if (curValue !== null) {
+            curValue.add(Pair(i, j))
+        }
+    }
+}
+
+val antiNodes = hashSetOf<Pair<Int, Int>>()
+frequencies.forEach { (_, points) ->
+    points.forEach outer@{ point1 ->
+        points.forEach { point2 ->
+            if (point1 == point2) return@outer
+            val dRow = (point1.first - point2.first)
+            val dCol = (point1.second - point2.second)
+
+            var curRow = point1.first
+            var curCol = point1.second
+            while (curRow in 0..<gridHeight && curCol in 0..<gridWidth) {
+                antiNodes.add(Pair(curRow, curCol))
+                curRow += dRow
+                curCol += dCol
+            }
+
+            curRow = point2.first
+            curCol = point2.second
+            while (curRow in 0..<gridHeight && curCol in 0..<gridWidth) {
+                antiNodes.add(Pair(curRow, curCol))
+                curRow -= dRow
+                curCol -= dCol
+            }
+        }
+    }
+}
+
+println(antiNodes.size)