advent-of-code/2021/nim/day15.nim

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import ./common, std/[sequtils, algorithm, sugar, sets, strformat, strutils, tables]
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type
Coordinate = uint
Cost = uint
Node = (Coordinate, Coordinate)
NodeSet = HashSet[Node]
Grid = Table[Node, Cost]
proc digitToUint(c: char): Cost = c.uint - '0'.uint
proc toGrid(input: Lines): (Grid, Coordinate, Coordinate) =
for y, line in input.pairs:
for x, c in line:
result[1] = max(x.uint + 1, result[1])
result[2] = max(y.uint + 1, result[2])
result[0][(x.uint, y.uint)] = c.digitToUint
proc lowest(nodes: NodeSet, scores: Grid): Node =
var lowest = uint.high
for n in nodes:
let score = scores.getOrDefault(n, uint.high)
if score < lowest:
result = n
lowest = score
proc astarCost(grid: Grid, start: Node, goal: Node, w: Coordinate, h: Coordinate, heuristic: (Node) -> Cost): Cost =
var open: NodeSet = [start].toHashSet
var cameFrom = initTable[Node, Node]()
var bestScores: Grid = {start: start.heuristic}.toTable
var guessScores: Grid = {start: start.heuristic}.toTable
while open.len() > 0:
var (x, y) = open.lowest guessScores
if (x, y) == goal:
var walker = goal
while cameFrom.contains(walker):
result += walker.heuristic
walker = cameFrom[walker]
return
open.excl (x, y)
for neighbor in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
if uint.high == neighbor[0] or uint.high == neighbor[1] or w == neighbor[0] or h == neighbor[1]: continue
# TODO: could this overflow?
var maybeBestScore = bestScores[(x, y)] + neighbor.heuristic
if maybeBestScore < bestScores.getOrDefault(neighbor, uint.high):
cameFrom[neighbor] = (x, y)
bestScores[neighbor] = maybeBestScore
guessScores[neighbor] = maybeBestScore + neighbor.heuristic
if not open.contains(neighbor):
open.incl(neighbor)
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proc p1(input: Lines): uint64 =
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let (grid, w, h) = input.toGrid
let heuristic = (n: Node) => grid[n]
let start: Node = (0'u, 0'u)
let goal: Node = (w - 1, h - 1)
astarCost(grid, start, goal, w, h, heuristic)
proc p2(input: Lines): uint64 =
let (mainTile, mtw, mth) = input.toGrid
var grid: Grid = initTable[Node, Cost]()
for tx in 0'u..<5'u:
for ty in 0'u..<5'u:
for x in 0'u..<mtw:
for y in 0'u..<mth:
let (ax, ay) = ((mtw * tx) + x, (mth * ty) + y)
var c = mainTile[(x, y)] + tx + ty
if c > 9: c -= 9
grid[(ax, ay)] = c
let (w, h) = (mtw * 5'u, mth * 5'u)
let heuristic = (n: Node) => grid[n]
let start: Node = (0'u, 0'u)
let goal: Node = (w - 1, h - 1)
astarCost(grid, start, goal, w, h, heuristic)
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const input = """
1163751742
1381373672
2136511328
3694931569
7463417111
1319128137
1359912421
3125421639
1293138521
2311944581
""".strip().split('\n').mapIt(it.strip)
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doDayX 15, (n: int) => n.loadInput, p1, p2, (input, 40'u64, 315'u64)