advent-of-code/2021/nim/day12.nim

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import ./common, std/[sequtils, algorithm, sugar, sets, strformat, strutils, tables]
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type
Lines = seq[string]
Path = seq[string]
NodeSet = HashSet[string]
Graph = Table[string, NodeSet]
proc toGraph(lines: Lines): Graph =
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for l in lines:
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let nodes = l.split "-"
if result.hasKey nodes[0]: result[nodes[0]].incl nodes[1]
else: result[nodes[0]] = toHashSet [nodes[1]]
if result.hasKey nodes[1]: result[nodes[1]].incl nodes[0]
else: result[nodes[1]] = toHashSet [nodes[0]]
proc basicIneligibleNodes(path: Path): NodeSet =
for n in path:
if n in ["start", "end"] or n.toUpper != n:
result.incl n
proc part2IneligibleNodes(path: Path): NodeSet =
# determine if we've double visited any small caves yet
var hasVisitedSingleSmallCaveTwice: bool = path.filterIt(not (it in ["start", "end"]) and it != it.toUpper).toCountTable.values.toSeq.anyIt(it >= 2)
for n in path:
let isStartOrEnd = n == "start" or n == "end"
let isSmall = n.toUpper != n
if isStartOrEnd or (isSmall and hasVisitedSingleSmallCaveTwice): result.incl n
# TODO: tail-call optimization?
proc visit(node: string, graph: Graph, ineligibleNodesReducer: (Path) -> NodeSet, path: Path = @[]): int =
if node == "end": return 1
let newPath = path & @[node]
let forbiddenNodes = newPath.ineligibleNodesReducer()
let toVisit = graph[node] - forbiddenNodes
for n in toVisit: result += visit(n, graph, ineligibleNodesReducer, newPath)
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proc pathing(input: seq[string]): int =
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visit("start", input.toGraph, basicIneligibleNodes)
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proc pathing2(input: seq[string]): int =
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visit("start", input.toGraph, part2IneligibleNodes)
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const smallTestInput = @[
"start-A",
"start-b",
"A-c",
"A-b",
"b-d",
"A-end",
"b-end",
]
const stest = (smallTestInput, 10, 36)
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# const largeTestInput = @[
# "fs-end",
# "he-DX",
# "fs-he",
# "start-DX",
# "pj-DX",
# "end-zg",
# "zg-sl",
# "zg-pj",
# "pj-he",
# "RW-he",
# "fs-DX",
# "pj-RW",
# "zg-RW",
# "start-pj",
# "he-WI",
# "zg-he",
# "pj-fs",
# "start-RW",
# ]
#
# const ltest = (largeTestInput, 225, 3509)
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doDay 12, n => n.loadInput, pathing, pathing2, stest