2023 Day 5 Part 1

2023/day05.nim

@@ -0,0 +1,88 @@
+import std/enumerate
+import std/math
+import std/sequtils
+import std/sets
+import std/strscans
+import std/strutils
+import std/sugar
+import std/tables
+
+type Remap = tuple
+  dst_start: int
+  src_start: int
+  length: int
+
+func parseRemap(s: string): Remap =
+  let parts = s.splitWhitespace.map(parseInt)
+  (parts[0], parts[1], parts[2])
+
+func includes(r: Remap, src: int): bool =
+  let range = r.src_start ..< (r.src_start + r.length)
+  src in range
+
+func lookup(r: Remap, src: int): int =
+  if r.includes(src):
+    return r.dst_start + (src - r.src_start)
+  src
+
+type Map = object
+  src: string
+  dst: string
+  remaps: seq[Remap]
+
+func parseMap(s: string): Map =
+  let lines = s.strip.splitLines
+  if not scanf(lines[0], "$+-to-$+ map:$.", result.src, result.dst):
+    raise newException(ValueError, lines[0])
+
+  for line in lines[1..^1]:
+    result.remaps.add parseRemap(line)
+
+func lookup(m: Map, src: int): int =
+  for remap in m.remaps:
+    if remap.includes(src):
+      return remap.lookup(src)
+  src
+
+type Almanac = tuple
+  seeds: HashSet[int]
+  mapsBySrc: Table[string, Map]
+  mapsByDst: Table[string, Map]
+
+func parseAlmanac(s: string): Almanac =
+  let sections = s.strip.split("\n\n")
+
+  var seeds: string
+  if not scanf(sections[0], "seeds: $*$.", seeds):
+    raise newException(ValueError, sections[0])
+
+  for num in seeds.strip.splitWhitespace:
+    result.seeds.incl num.parseInt
+
+  for section in sections[1..^1]:
+    let map = parseMap(section)
+    result.mapsBySrc[map.src] = map
+    result.mapsByDst[map.dst] = map
+
+func location(a: Almanac, seed: int): int =
+  var map = a.mapsBySrc["seed"]
+  var src = seed
+
+  while true:
+    src = map.lookup(src)
+    if map.dst == "location":
+      return src
+
+    map = a.mapsBySrc[map.dst]
+
+proc part1(): int =
+  let text = readFile("input/day05.txt")
+  let almanac = parseAlmanac(text)
+
+  let locations = collect(newSeq):
+    for seed in almanac.seeds:
+      almanac.location(seed)
+
+  locations.min
+
+echo part1()