From 4cd13c0129add03ca7bb6d26a12de6eebdf895de Mon Sep 17 00:00:00 2001
From: Sloane Perrault <sloane.perrault@gmail.com>
Date: Wed, 21 Sep 2022 09:19:52 -0400
Subject: [PATCH] solve: day 5

 - solve: day 5, part 1
 - solve: day 5, part 2
---
 2020/05/README.md |  9 +++++++++
 2020/05/day5.hs   | 28 ++++++++++++++++++++++++++++
 2020/05/part1.hs  |  9 +++++++++
 2020/05/part2.hs  | 14 ++++++++++++++
 4 files changed, 60 insertions(+)
 create mode 100644 2020/05/day5.hs
 create mode 100755 2020/05/part1.hs
 create mode 100755 2020/05/part2.hs

diff --git a/2020/05/README.md b/2020/05/README.md
index e69de29..e9468ba 100644
--- a/2020/05/README.md
+++ b/2020/05/README.md
@@ -0,0 +1,9 @@
+# Day 5
+
+## Part 1
+
+It's just binary where `F` and `L` are `0` and `B` and `R` are `1`.
+
+## Part 2
+
+At first I just looked at the difference between lists to get the answer. Since updated to find the first difference in the two lists (of all possible seats and the actual seats) after skipping the gap at the start.
diff --git a/2020/05/day5.hs b/2020/05/day5.hs
new file mode 100644
index 0000000..bf15928
--- /dev/null
+++ b/2020/05/day5.hs
@@ -0,0 +1,28 @@
+module Day5 (BoardingPass(BoardingPass), seatId) where
+
+data BoardingPass = BoardingPass { row :: Int, column :: Int }
+  deriving (Show)
+
+binaryStringToInt b = binaryStringToInt' (reverse b) 0 0
+  where
+    binaryStringToInt' [] _ acc = acc
+    binaryStringToInt' ('1':bs) m acc = binaryStringToInt' bs (m+1) (acc + 2^m)
+    binaryStringToInt' ('0':bs) m acc = binaryStringToInt' bs (m+1) acc
+
+charToBinaryDigit 'F' = '0'
+charToBinaryDigit 'L' = '0'
+charToBinaryDigit 'B' = '1'
+charToBinaryDigit 'R' = '1'
+
+stringToInt = binaryStringToInt . map charToBinaryDigit
+
+readBoardingPass str =
+    let (str', rest) = splitAt 10 str
+        (rowS, colS) = splitAt 7 str'
+    in
+        (BoardingPass (stringToInt rowS) (stringToInt colS), rest)
+
+instance Read BoardingPass where
+  readsPrec _ str = [readBoardingPass str]
+
+seatId (BoardingPass row column) = row * 8 + column
diff --git a/2020/05/part1.hs b/2020/05/part1.hs
new file mode 100755
index 0000000..d12c5bb
--- /dev/null
+++ b/2020/05/part1.hs
@@ -0,0 +1,9 @@
+#!/usr/bin/env runghc
+
+import Day5
+
+main = interact solve
+
+solve = show . maxSeatId . map (read :: String -> BoardingPass) . lines
+
+maxSeatId = maximum . map seatId
diff --git a/2020/05/part2.hs b/2020/05/part2.hs
new file mode 100755
index 0000000..8be8c42
--- /dev/null
+++ b/2020/05/part2.hs
@@ -0,0 +1,14 @@
+#!/usr/bin/env runghc
+
+import Day5
+import Data.List
+
+main = interact solve
+
+solve = show . mySeat . map (seatId . read) . lines
+
+mySeat input = mySeat'
+  where
+    boardingPasses = sort input
+    start = head boardingPasses
+    mySeat' = fst . head . dropWhile (uncurry (==)) $ zip [start..] boardingPasses