Day 3.

src/aoc2025/Day03.kt

@@ -0,0 +1,56 @@
+package aoc2025
+
+import println
+import readInput
+
+/*
+--- Day 3: Lobby ---
+https://adventofcode.com/2025/day/3
+*/
+fun main() {
+    val inlineTestInput = """
+987654321111111
+811111111111119
+234234234234278
+818181911112111
+"""
+
+    val powTenTable = generateSequence(1L) { it * 10L }.take(20).toList().toLongArray()
+
+    fun rec(i: String, si: Int, left: Int): Long {
+        for (dig in 9 downTo 1) {
+            val dp = i.indexOf('0' + dig, si)
+            if (dp >= 0) {
+                if (left == 0) {
+                    return dig.toLong()
+                } else {
+                    val lastDigits = rec(i, dp + 1, left - 1)
+                    if (lastDigits >= 0) return lastDigits + dig * powTenTable[left]
+                }
+            }
+        }
+        return -1L
+    }
+
+    fun part1(input: List<String>): Long {
+        return input.sumOf { rec(it, 0, 1) }
+    }
+
+    fun part2(input: List<String>): Long {
+        return input.sumOf { rec(it, 0, 11) }
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2025/Day03_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 357L)
+    check(testInputPart2Result == 3121910778619L)
+
+    val input = readInput("aoc2025/Day03")
+    part1(input).println()
+    part2(input).println()
+}