26

Day 5: Print Queue

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL

FAQ

you are viewing a single comment's thread
view the rest of the comments
[-] zarlin@lemmy.world 2 points 1 week ago

Nim

import ../aoc, strutils, sequtils, tables

type
  Rules = ref Table[int, seq[int]]

#check if an update sequence is valid
proc valid(update:seq[int], rules:Rules):bool =
  for pi, p in update:
    for r in rules.getOrDefault(p):
      let ri = update.find(r)
      if ri != -1 and ri < pi:
        return false
  return true

proc backtrack(p:int, index:int, update:seq[int], rules: Rules, sorted: var seq[int]):bool =
  if index == 0:
    sorted[index] = p
    return true
  
  for r in rules.getOrDefault(p):
    if r in update and r.backtrack(index-1, update, rules, sorted):
      sorted[index] = p
      return true
  
  return false

#fix an invalid sequence
proc fix(update:seq[int], rules: Rules):seq[int] =
  echo "fixing", update
  var sorted = newSeqWith(update.len, 0);
  for p in update:
    if p.backtrack(update.len-1, update, rules, sorted):
      return sorted
  return @[]

proc solve*(input:string): array[2,int] =
  let parts = input.split("\r\n\r\n");
  
  let rulePairs = parts[0].splitLines.mapIt(it.strip.split('|').map(parseInt))
  let updates = parts[1].splitLines.mapIt(it.split(',').map(parseInt))
  
  # fill rules table
  var rules = new Rules
  for rp in rulePairs:
    if rules.hasKey(rp[0]):
      rules[rp[0]].add rp[1];
    else:
      rules[rp[0]] = @[rp[1]]
      
  # fill reverse rules table
  var backRules = new Rules
  for rp in rulePairs:
    if backRules.hasKey(rp[1]):
      backRules[rp[1]].add rp[0];
    else:
      backRules[rp[1]] = @[rp[0]]
  
  for u in updates:
    if u.valid(rules):
      result[0] += u[u.len div 2]
    else:
      let uf = u.fix(backRules)
      result[1] += uf[uf.len div 2]

I thought of doing a sort at first, but dismissed it for some reason, so I came up with this slow and bulky recursive backtracking thing which traverses the rules as a graph until it reaches a depth equal to the given sequence. Not my finest work, but it does solve the puzzle :)

this post was submitted on 05 Dec 2024
26 points (100.0% liked)

Advent Of Code

920 readers
57 users here now

An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2024

Solution Threads

M T W T F S S
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25

Rules/Guidelines

Relevant Communities

Relevant Links

Credits

Icon base by Lorc under CC BY 3.0 with modifications to add a gradient

console.log('Hello World')

founded 1 year ago
MODERATORS