advent-of-code/2024/day-6/solution-1.sh

#!/usr/bin/env bash

ARRAY_SHAPE=130 # It's a square
FILENAME=input
read -r -a MAP_ARRAY <<< "$( paste -s -d '' "$FILENAME" | sed -E 's/(.)/\1\ /g' )"

# Get initial position
POSITION=$(( ( $( grep -n '\^' "$FILENAME" | cut -f1 -d: ) -1 ) * ARRAY_SHAPE -1 + $( grep -o '.*\^' "$FILENAME" | wc -c ) -1 ))
MAP_ARRAY[POSITION]=X # Remove position after save

# up = 0, right = 1, down = 2, left = 3, following 90 degree turn
TURNS=0
while true
do
  EXIT=1

  # Get direction and travel 
  DIRECTION=$(( TURNS % 4 ))
  if [[ $DIRECTION -eq 0 ]] # up
  then
    TRAVEL=-$ARRAY_SHAPE
    LIMIT=$(( POSITION % ARRAY_SHAPE ))
  elif [[ $DIRECTION -eq 1 ]] # right
  then
    TRAVEL=1
    LIMIT=$(( (POSITION / ARRAY_SHAPE + 1) * ARRAY_SHAPE )) # Never verified
  elif [[ $DIRECTION -eq 2 ]] # down
  then
    TRAVEL=$ARRAY_SHAPE
    LIMIT=$(( (POSITION % ARRAY_SHAPE) + (ARRAY_SHAPE * ARRAY_SHAPE) ))
  elif [[ $DIRECTION -eq 3 ]] # left
  then
    TRAVEL=-1
    LIMIT=$(( (POSITION / ARRAY_SHAPE) * ARRAY_SHAPE )) # Never verified
  fi

  while [[ ${MAP_ARRAY[$POSITION+$TRAVEL]} != '#' ]]
  do
    if [[ $POSITION -eq $LIMIT ]] # Walked out
    then
      EXIT=0
      break
    fi

    MAP_ARRAY[POSITION]=X # Mark walking path
    (( POSITION+=TRAVEL ))
  done
  
  if [[ $EXIT -eq 0 ]] ; then break ; fi # Walked out

  (( TURNS++ ))
done

# Count all coordinates
printf "%s" "${MAP_ARRAY[@]}" | tee travel-path | sed 's/[^X]//g' | wc -c
< travel-path fold -w $ARRAY_SHAPE