Finished 2024 day 7 both parts

2024/kotlin/src/main/kotlin/Main.kt

@@ -6,6 +6,7 @@ import com.tymscar.day03.solve as day03
 import com.tymscar.day04.solve as day04
 import com.tymscar.day05.solve as day05
 import com.tymscar.day06.solve as day06
+import com.tymscar.day07.solve as day07
 
 fun main() {
     day01()
@@ -14,4 +15,5 @@ fun main() {
     day04()
     day05()
     day06()
+    day07()
 }

2024/kotlin/src/main/kotlin/com/tymscar/day07/part1/part1.kt

@@ -1,5 +1,20 @@
 package com.tymscar.day07.part1
 
+private fun isValid(solution: Long, equation: List<Long>): Boolean {
+    if (equation.isEmpty()) return solution == 0L
+    val sumSolution = isValid(solution - equation.first(), equation.drop(1))
+    val multSolution =
+        if (solution % equation.first() == 0L) isValid(solution / equation.first(), equation.drop(1)) else false
+    return sumSolution || multSolution
+}
+
 fun solve(input: String): String {
-    return input
+    var equations = input.lines().map {
+        Regex("""(\d+)""").findAll(it).map { it.value.toLong() }.toList()
+    }
+
+    return equations
+        .filter { isValid(it.first(), it.drop(1).reversed()) }
+        .sumOf { it.first() }
+        .toString()
 }

2024/kotlin/src/main/kotlin/com/tymscar/day07/part2/part2.kt

@@ -1,5 +1,34 @@
 package com.tymscar.day07.part2
 
+import kotlin.math.floor
+import kotlin.math.log10
+import kotlin.math.pow
+
+private fun deconcat(log: Long, splinter: Long): Long? {
+    val splinterSizeInHundreds = 10.0.pow(floor(log10(splinter.toDouble())) + 1).toLong()
+    val afterDeconcat: Long = log / splinterSizeInHundreds
+    return if ((afterDeconcat * splinterSizeInHundreds + splinter) == log) afterDeconcat else null
+}
+
+private fun isValid(solution: Long?, equation: List<Long>): Boolean {
+    if (solution == null) return false
+    if (equation.isEmpty()) return solution == 0L
+    val remainingEq = equation.drop(1)
+    val sumSolution = isValid(solution - equation.first(), remainingEq)
+    val multSolution =
+        if (solution % equation.first() == 0L) isValid(solution / equation.first(), remainingEq) else false
+    val concatSolution =
+        isValid(deconcat(solution, equation.first()), remainingEq)
+    return sumSolution || multSolution || concatSolution
+}
+
 fun solve(input: String): String {
-    return input
+    var equations = input.lines().map {
+        Regex("""(\d+)""").findAll(it).map { it.value.toLong() }.toList()
+    }
+
+    return equations
+        .filter { isValid(it.first(), it.drop(1).reversed()) }
+        .sumOf { it.first() }
+        .toString()
 }