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diff --git a/‎src/main/kotlin/advent2021/Day04.kt
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+package advent2021
+
+typealias BingoBoard = List<List<Int>>
+
+class Day04(input: List<String>) {
+
+    private val draws: List<Int> = input.first().split(",").map { it.toInt() }
+    private val boards: Set<BingoBoard> = parseInput(input)
+
+    fun solvePart1(): Int {
+        val drawn = draws.take(4).toMutableSet()
+        return draws.drop(4).firstNotNullOf { draw ->
+            drawn += draw
+            boards.firstOrNull { it.isWinner(drawn) }?.let { winner ->
+                draw * winner.sumUnmarked(drawn)
+            }
+        }
+    }
+
+    fun solvePart2(): Int {
+        val drawn = draws.toMutableSet()
+        return draws.reversed().firstNotNullOf { draw ->
+            drawn -= draw
+            boards.firstOrNull { !it.isWinner(drawn) }?.let { winner ->
+                draw * (winner.sumUnmarked(drawn) - draw)
+            }
+        }
+    }
+
+    private fun BingoBoard.isWinner(draws: Set<Int>) =
+        this.any { row -> row.all { it in draws } } ||
+                (0..4).any { col -> this.all { row -> row[col] in draws } }
+
+    private fun BingoBoard.sumUnmarked(draws: Set<Int>): Int =
+        this.sumOf { row ->
+            row.filterNot { it in draws }.sum()
+        }
+
+    private fun parseInput(input: List<String>): Set<BingoBoard> =
+        input
+            .asSequence()
+            .drop(1)
+            .filter { it.isNotEmpty() }
+            .chunked(5)
+            .map { parseSingleBoard(it) }
+            .toSet()
+
+    private fun parseSingleBoard(input: List<String>): BingoBoard =
+        input.map { row ->
+            row.split(" ").filter { it.isNotEmpty() }.map { it.toInt() }
+        }
+}
+
+fun main() {
+    val input = Resources.resourceAsListOfString("advent2021/day04.txt")
+    val day = Day04(input = input)
+    println("Part 1: ${day.solvePart1()}")
+    println("Part 2: ${day.solvePart2()}")
+}