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diff --git a/‎src/main/kotlin/advent2021/Day03.kt
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+package advent2021
+
+import Resources
+import kotlin.math.pow
+
+class Day03(private val input: List<String>) {
+
+    private val inputWidth = input.first().length
+
+    fun solvePart1(): Int {
+        val gamma = (0 until inputWidth).sumOf { column ->
+            val columnValue = (inputWidth - column - 1).binaryColumnValue()
+            if (input.count { it[column] == '1' } > input.size / 2) columnValue else 0
+        }
+        return gamma * (inputWidth.maxBinaryValue() - gamma)
+    }
+
+    private fun Int.binaryColumnValue(): Int =
+        2.0.pow(this.toDouble()).toInt()
+
+    private fun Int.maxBinaryValue(): Int =
+        binaryColumnValue() - 1
+
+    fun solvePart2(): Int =
+        input.bitwiseFilter(true).toInt(2) * input.bitwiseFilter(false).toInt(2)
+
+    private fun List<String>.bitwiseFilter(keepMostCommon: Boolean): String =
+        (0 until inputWidth).fold(this) { inputs, column ->
+            if (inputs.size == 1) inputs else {
+                val split = inputs.partition { it[column] == '1' }
+                if (keepMostCommon) split.longest() else split.shortest()
+            }
+        }.first()
+
+    private fun <T> Pair<List<T>,List<T>>.longest(): List<T> =
+        if(first.size >= second.size) first else second
+
+    private fun <T> Pair<List<T>,List<T>>.shortest(): List<T> =
+        if(first.size < second.size) first else second
+}
+
+fun main() {
+    val input = Resources.resourceAsListOfString("advent2021/day03.txt")
+    val day = Day03(input = input)
+    println("Part 1: ${day.solvePart1()}")
+    println("Part 2: ${day.solvePart2()}")
+}