2023 Day 10 Part 1

2023/day10.nim

@@ -0,0 +1,99 @@
+import std/algorithm
+import std/deques
+import std/enumerate
+import std/math
+import std/sequtils
+import std/sets
+import std/strscans
+import std/strutils
+import std/sugar
+import std/tables
+
+proc dbg[T](v: T): T = (echo(v); v)
+
+type Point = tuple
+  r: int
+  c: int
+
+type Sketch = object
+  rows: int
+  cols: int
+  start: (int, int)
+  grid: Table[Point, char]
+
+func parseSketch(text: string): Sketch =
+  let lines = text.strip.splitLines()
+  result.rows = lines.len
+  result.cols = lines[0].len
+
+  for (r, line) in enumerate(lines):
+    for (c, sym) in enumerate(line):
+      result.grid[(r, c)] = sym
+
+      if sym == 'S':
+        result.start = (r, c)
+
+func pipeAt(s: Sketch, p: Point): char =
+  if p.r in 0 ..< s.rows and p.c in 0 ..< s.cols:
+    s.grid[p]
+  else:
+    '.'
+
+type Direction = enum
+  N
+  S
+  E
+  W
+
+proc hasConn(s: Sketch, p: Point, d: Direction): bool =
+  case s.pipeAt(p):
+    of 'S': true
+    of '.': false
+    of '|': d in [N, S]
+    of '-': d in [W, E]
+    of 'L': d in [N, E]
+    of 'J': d in [N, W]
+    of '7': d in [W, S]
+    of 'F': d in [E, S]
+    else: raise newException(ValueError, $s.grid[p])
+
+func neighbors(s: Sketch, p: Point): seq[Point] =
+  for (dr, dc, pDir, nDir) in [
+    (-1, 0, N, S), # Up     N-S
+    (+1, 0, S, N), # Down   S-N
+    (0, -1, W, E), # Left   W-E
+    (0, +1, E, W), # Right  E-W
+  ]:
+    let n = (p.r + dr, p.c + dc)
+    if s.hasConn(p, pDir) and s.hasConn(n, nDir):
+      result.add(n)
+
+type State = tuple
+  point: Point
+  distance: int
+
+proc reachable(s: Sketch): Table[Point, int] =
+  var queue: Deque[State]
+  var seen: HashSet[Point]
+
+  queue.addLast (s.start, 0)
+
+  while queue.len > 0:
+    let state = queue.popFirst
+    if state.point in seen:
+      continue
+
+    result[state.point] = state.distance
+    seen.incl state.point
+
+    for n in s.neighbors(state.point):
+      queue.addLast (n, state.distance + 1)
+
+proc part1(): int =
+  let text = readFile("input/day10.txt")
+  let sketch = parseSketch(text)
+
+  for d in values(sketch.reachable):
+    result = max(result, d)
+
+echo part1()