2023 Day 13 Part 1

2023/day13.nim

@@ -0,0 +1,98 @@
+import std/algorithm
+import std/deques
+import std/enumerate
+import std/math
+import std/options
+import std/sequtils
+import std/sets
+import std/strscans
+import std/strutils
+import std/sugar
+import std/tables
+import std/terminal
+
+proc dbg[T](v: T): T = (echo(v); v)
+
+func empty[T](v: seq[T]): bool = v.len == 0
+
+type Point = tuple
+  r: int
+  c: int
+
+type Pattern = object
+  height: int
+  width: int
+
+  grid: Table[Point, char]
+
+  rows: seq[seq[char]]
+  cols: seq[seq[char]]
+
+func parsePattern(text: string): Pattern =
+  let lines = text.strip.splitLines()
+  result.height = lines.len
+  result.width = lines[0].len
+
+  for r in 0 ..< result.height:
+    result.rows.add @[]
+
+  for c in 0 ..< result.width:
+    result.cols.add @[]
+
+  for (r, line) in enumerate(lines):
+    for (c, sym) in enumerate(line):
+      result.grid[(r, c)] = sym
+      result.rows[r] &= @[sym]
+      result.cols[c] &= @[sym]
+
+func parsePatterns(text: string): seq[Pattern] =
+  text.strip.split("\n\n").map(parsePattern)
+
+func col(p: Pattern, c: int): (seq[char], bool) =
+  if c in p.cols.low .. p.cols.high:
+    (p.cols[c], true)
+  else:
+    (@[], false)
+
+func row(p: Pattern, r: int): (seq[char], bool) =
+  if r in p.rows.low .. p.rows.high:
+    (p.rows[r], true)
+  else:
+    (@[], false)
+
+proc reflectAtV(p: Pattern, c: int): bool =
+  for dc in 0 .. c:
+    let (l, okL) = p.col(c-dc - 1)
+    let (r, okR) = p.col(c+dc)
+    if okL and okR and l != r:
+      return false
+  true
+
+proc reflectAtH(p: Pattern, r: int): bool =
+  for dr in 0 ..< r:
+    let (u, okU) = p.row(r-dr - 1)
+    let (d, okD) = p.row(r+dr)
+    if okU and okD and d != u:
+      return false
+  true
+
+proc reflectVertical(p: Pattern): int =
+  for c in 1 ..< p.width:
+    if p.reflectAtV(c):
+      return c
+
+proc reflectHorizontal(p: Pattern): int =
+  for r in 1 ..< p.height:
+    if p.reflectAtH(r):
+      return r
+
+proc part1(input: string): int =
+  let text = readFile(input)
+  let patterns = parsePatterns(text)
+
+  for pattern in patterns:
+    result.inc pattern.reflectVertical
+    result.inc 100 * pattern.reflectHorizontal
+
+echo part1("input/test.txt")
+echo part1("input/day13.txt")