2023 - Day 13 - part 2 - with help from ephemient - my logic didn't w…

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fmmr · Dec 13, 2023 · 7e1e9f7 · 7e1e9f7
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diff --git a/src/main/kotlin/no/rodland/advent_2023/Day13.kt b/src/main/kotlin/no/rodland/advent_2023/Day13.kt
@@ -1,65 +1,77 @@
 package no.rodland.advent_2023
 
 import no.rodland.advent.Day
+import java.lang.Integer.min
 
 // template generated: 13/12/2023
 // Fredrik Rødland 2023
 
-class Day13(val input: List<String>) : Day<Int, Long, List<Day13.GroundMap>> {
+class Day13(val input: List<String>) : Day<Int, Int, List<Day13.GroundMap>> {
 
     private val parsed = input.parse()
 
     override fun partOne(): Int {
-        return parsed.map { groundMap ->
-            val rowsHorizontal = isMirror(groundMap)
-            val rowsVertical = if (rowsHorizontal == 0) {
-                isMirror(groundMap.transpose())
-            } else {
-                0
-            }
-//            debug(rowsVertical, rowsHorisontal, groundMap)
-            rowsVertical + 100 * rowsHorizontal
-        }.sum()
+        return run(::partOneCompare)
+    }
+
+    override fun partTwo(): Int {
+        return run(::partTwoCompare)
     }
 
-    private fun debug(rowsVertical: Int, rowsHorisontal: Int, groundMap: GroundMap) {
-        if (rowsVertical == 0 && rowsHorisontal == 0) {
-            println("no reflection for:")
+    private fun run(compare: (List<String>, List<String>) -> Boolean) = parsed.sumOf { groundMap ->
+        val rowsHorizontal = isMirror(groundMap, compare)
+        val rowsVertical = if (rowsHorizontal == 0) {
+            isMirror(groundMap.transpose(), compare)
         } else {
-            println("misc v: $rowsVertical, h: $rowsHorisontal")
+            0
         }
-        groundMap.print()
-        println()
+        rowsVertical + 100 * rowsHorizontal
     }
 
-    // 1500 too low
-    // 1700 too low
-    private fun isMirror(groundMap: GroundMap): Int {
+    private fun isMirror(groundMap: GroundMap, compare: (List<String>, List<String>) -> Boolean): Int {
         (1..<groundMap.size).forEach { i ->
             val map = groundMap.grounds
 
             val rev = map.subList(0, i).asReversed()
             val forw = map.subList(i, map.size)
 
-            val size = minOf(rev.size, forw.size)
             // println("rev:   $rev    for:    $forw")
-            if (rev.subList(0, size) == forw.subList(0, size))
-                return i
+            val b = compare(rev, forw)
+            if (b) return i
         }
         return 0
     }
 
-    override fun partTwo(): Long {
-        return 2
+    private fun partOneCompare(reverseList: List<String>, forwardList: List<String>): Boolean {
+        val size = min(reverseList.size, forwardList.size)
+        return reverseList.subList(0, size) == forwardList.subList(0, size)
     }
 
-    override fun List<String>.parse(): List<GroundMap> {
-        val converters = joinToString("\n").split("\n\n").map { it.split("\n") }
-
-        return converters.map { l ->
-            GroundMap(l)
+    // https://github.com/ephemient/aoc2023/blob/main/kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day13.kt
+    private fun partTwoCompare(reverseList: List<String>, forwardList: List<String>): Boolean {
+        val size = min(reverseList.size, forwardList.size)
+        var almostEqual = false
+
+        // hm - this didn't work for some reason - so...
+        // var diffCount = 0
+        // for (i in 0..<size) {
+        //     if (reverseList[i] != forwardList[i]) {
+        //         diffCount++
+        //     }
+        // }
+        // ..."borrowing" the followign code from ephemient
+        for (i in 0..<size) {
+            val a = reverseList[i]
+            val b = forwardList[i]
+            val delta = a.indices.count { a[it] != b[it] }
+            if (delta > 1) return false
+            if (delta == 1) if (almostEqual) return false else almostEqual = true
         }
+        return almostEqual
+    }
 
+    override fun List<String>.parse(): List<GroundMap> {
+        return joinToString("\n").split("\n\n").map { it.split("\n") }.map { l -> GroundMap(l) }
     }
 
     data class GroundMap(val grounds: List<String>) {

diff --git a/src/test/kotlin/no/rodland/advent_2023/Day13Test.kt b/src/test/kotlin/no/rodland/advent_2023/Day13Test.kt
@@ -16,9 +16,9 @@ internal class Day13Test {
     private val test13 = "2023/input_13_test.txt".readFile()
 
     private val resultTestOne = 405
-    private val resultTestTwo = 2L
+    private val resultTestTwo = 400
     private val resultOne = 40006
-    private val resultTwo = 2L
+    private val resultTwo = 28627
 
     val test = defaultTestSuiteParseOnInit(
         Day13(data13),
@@ -29,7 +29,8 @@ internal class Day13Test {
         resultTwo,
         { Day13(data13) },
         { Day13(test13) },
-        numTestPart1 = 300
+        numTestPart1 = 300,
+        numTestPart2 = 300
     )
 
     @Nested