From 91e5a765ec66409b0625c187b973eccb92890cbf Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Fri, 10 Dec 2021 06:29:11 +0100
Subject: [PATCH] day(10): add solution

Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 src/year2021/day10/Day10.kt   | 74 +++++++++++++++++++++++++++++++++++
 src/year2021/day10/sample.txt | 10 +++++
 2 files changed, 84 insertions(+)
 create mode 100644 src/year2021/day10/Day10.kt
 create mode 100644 src/year2021/day10/sample.txt

diff --git a/src/year2021/day10/Day10.kt b/src/year2021/day10/Day10.kt
new file mode 100644
index 0000000..ead3a24
--- /dev/null
+++ b/src/year2021/day10/Day10.kt
@@ -0,0 +1,74 @@
+package year2021.day10
+
+import readInput
+
+val CLOSING: Map<Char, Char> = mapOf(
+    ')' to '(',
+    ']' to '[',
+    '}' to '{',
+    '>' to '<'
+)
+val ERROR_SCORING: Map<Char, Int> = mapOf(')' to 3, ']' to 57, '}' to 1197, '>' to 25137)
+val AUTOCOMPLETE_SCORING: Map<Char, Long> = mapOf(
+    '(' to 1,
+    '[' to 2,
+    '{' to 3,
+    '<' to 4
+)
+
+fun firstInvalid(input: String): Char? {
+    val stack = mutableListOf<Char>()
+
+    for (c in input) {
+        if (CLOSING.contains(c)) {
+            // found a closing one
+            if (stack.size < 1 || stack.last() != CLOSING[c]) {
+                return c
+            }
+            stack.removeLast()
+        } else {
+            stack.add(c)
+        }
+    }
+    return null
+}
+
+fun part1(input: List<String>): Int = input.sumOf {
+    firstInvalid(it)?.let { c ->
+        ERROR_SCORING[c]
+    } ?: 0
+}
+
+fun getRemaining(input: String): List<Char> {
+    val stack = mutableListOf<Char>()
+
+    for (c in input) {
+        if (CLOSING.contains(c)) {
+            stack.removeLast()
+        } else {
+            stack.add(c)
+        }
+    }
+
+    return stack
+}
+
+fun part2(input: List<String>): Long = input
+    .filter { firstInvalid(it) == null }
+    .map {
+        getRemaining(it).reversed().fold(0.toLong()) { total, c -> 5 * total + AUTOCOMPLETE_SCORING[c]!! }
+    }
+    .sorted().let { scores ->
+        scores[scores.size / 2]
+    }
+
+fun main() {
+    val sample = readInput(10, "sample")
+    val input = readInput(10, "input")
+
+    check(part1(sample) == 26397)
+    println(part1(input))
+
+    check(part2(sample) == 288957.toLong())
+    println(part2(input))
+}
diff --git a/src/year2021/day10/sample.txt b/src/year2021/day10/sample.txt
new file mode 100644
index 0000000..2f182d8
--- /dev/null
+++ b/src/year2021/day10/sample.txt
@@ -0,0 +1,10 @@
+[({(<(())[]>[[{[]{<()<>>
+[(()[<>])]({[<{<<[]>>(
+{([(<{}[<>[]}>{[]{[(<()>
+(((({<>}<{<{<>}{[]{[]{}
+[[<[([]))<([[{}[[()]]]
+[{[{({}]{}}([{[{{{}}([]
+{<[[]]>}<{[{[{[]{()[[[]
+[<(<(<(<{}))><([]([]()
+<{([([[(<>()){}]>(<<{{
+<{([{{}}[<[[[<>{}]]]>[]]
\ No newline at end of file