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# Day 9: Rope Bridge
import std/[os, strutils, sequtils, sets]
let input = paramStr(1).readFile().strip().split("\n")
let directions = input.mapIt(it.split(" ")).mapIt((it[0][0], it[1].parseInt()))
type Pos = ref object # must be ref for mutation
x: int
y: int
type Knot = ref object
pos: Pos
prev: Knot
func init(_: typedesc[Knot], prev: Knot): Knot =
return Knot(pos: Pos(x: 0, y: 0), prev: prev)
proc update(loc, knot: Knot) =
let dx = loc.pos.x - knot.pos.x
let dy = loc.pos.y - knot.pos.y
if abs(dx) == 2:
knot.pos.x += dx div 2
if dy != 0:
knot.pos.y += dy div abs(dy)
elif abs(dy) == 2:
knot.pos.y += dy div 2
if dx != 0:
knot.pos.x += dx div abs(dx)
proc update(knots: varargs[Knot]) =
for i, knot in knots:
update(knot.prev, knot)
var visited = initHashSet[(int, int)]()
var visitedAgain = initHashSet[(int, int)]()
var
head = Knot.init(nil)
tail = Knot.init(head)
var
one = Knot.init(head)
two = Knot.init(one)
three = Knot.init(two)
four = Knot.init(three)
five = Knot.init(four)
six = Knot.init(five)
seven = Knot.init(six)
eight = Knot.init(seven)
nine = Knot.init(eight)
for dir in directions:
for i in 0 ..< dir[1]:
if dir[0] == 'R': head.pos.x += 1
elif dir[0] == 'L': head.pos.x -= 1
elif dir[0] == 'U': head.pos.y += 1
elif dir[0] == 'D': head.pos.y -= 1
update(head, tail)
visited.incl((tail.pos.x, tail.pos.y))
update(one, two, three, four, five, six, seven, eight, nine)
visitedAgain.incl((nine.pos.x, nine.pos.y))
echo visited.len
echo visitedAgain.len
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