From b414a9d34901a9296d12d5257d5be62a487d1d30 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Sun, 17 Dec 2023 13:56:50 -0800
Subject: [PATCH] 2023 Day 17 Part 1

---
 2023/day17.nim | 147 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 2023/day17.nim

diff --git a/2023/day17.nim b/2023/day17.nim
new file mode 100644
index 0000000..7f02280
--- /dev/null
+++ b/2023/day17.nim
@@ -0,0 +1,147 @@
+import std/algorithm
+import std/deques
+import std/enumerate
+import std/heapqueue
+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
+import std/times
+
+proc dbg[T](v: T): T = (echo(v); v)
+
+func empty[T](v: seq[T]): bool = v.len == 0
+
+proc split[T](v: seq[T], pred: proc(elt: T): bool {.noSideEffect.}): seq[seq[T]] =
+  var current: seq[T]
+  for elt in v:
+    if pred(elt):
+      result.add current
+      current = @[]
+    else:
+      current.add elt
+  result.add current
+
+func join[T](parts: seq[seq[T]], sep: T): seq[T] =
+  if parts.len > 0:
+    result &= parts[0]
+
+  for part in parts[1..^1]:
+    result.add sep
+    result &= part
+
+type Point = tuple
+  r: int
+  c: int
+
+type Map = object
+  height: int
+  width: int
+  grid: Table[Point, int]
+
+func parseMap(text: string): Map =
+  let lines = text.strip.splitLines()
+  result.height = lines.len
+  result.width = lines[0].len
+
+  for (r, line) in enumerate(lines):
+    for (c, sym) in enumerate(line):
+      result.grid[(r, c)] = sym.int - '0'.int
+
+type Direction = enum
+  N
+  W
+  S
+  E
+
+func cw(d: Direction): Direction =
+  case d:
+    of N: E
+    of E: S
+    of S: W
+    of W: N
+
+func ccw(d: Direction): Direction =
+  case d:
+    of N: W
+    of W: S
+    of S: E
+    of E: N
+
+func move(p: Point, d: Direction, n: int): Point =
+  case d:
+    of N: (p.r - n, p.c)
+    of S: (p.r + n, p.c)
+    of W: (p.r, p.c - n)
+    of E: (p.r, p.c + n)
+
+func inBounds(m: Map, p: Point): bool =
+  p.r in 0 ..< m.height and p.c in 0 ..< m.width
+
+func loss(m: Map, p: Point): int =
+  if m.inBounds(p):
+    return m.grid[p]
+
+type State = tuple
+  pos: Point
+  dir: Direction
+
+type Node = tuple
+  state: State
+  cost: int
+
+func `<`(a, b: Node): bool = a.cost < b.cost
+
+
+iterator successors(m: Map, state: State): (State, int) =
+  for steps in 1..3:
+    var pos = state.pos
+    var loss = 0
+    for _ in 1..steps:
+      pos = pos.move(state.dir, 1)
+      loss += m.loss(pos)
+
+    yield ((pos, state.dir.cw), loss)
+    yield ((pos, state.dir.ccw), loss)
+
+proc heatLoss(m: Map, start, goal: Point): int =
+  var queue: HeapQueue[Node]
+  var seen: HashSet[State]
+
+  # Unknown starting direction, so try them all.
+  queue.push ((start, N), 0)
+  queue.push ((start, S), 0)
+  queue.push ((start, E), 0)
+  queue.push ((start, W), 0)
+
+  while queue.len > 0:
+    let (state, cost) = queue.pop
+
+    if not m.inBounds(state.pos): continue
+
+    if state in seen: continue
+    seen.incl state
+
+    if state.pos == goal:
+      return cost
+
+    for (next, extra) in m.successors(state):
+      queue.push (next, cost + extra)
+
+proc part1(input: string): int =
+  let text = readFile(input)
+  let map = parseMap(text)
+  map.heatLoss((0, 0), (map.height - 1, map.width - 1))
+
+proc timed[T](f: () -> T): T =
+  let start = cpuTime()
+  result = f()
+  echo "Time :", cpuTime() - start
+
+echo timed(proc(): int = part1("input/test.txt"))
+echo timed(proc(): int = part1("input/day17.txt"))