#!/bin/bash

declare -A transitions
while read line; do
  first=$(sed 's/-.*$//' <<< $line)
  last=$(sed 's/^.*-//' <<< $line)
  transitions[$first]=${transitions[$first]}','$last','
  transitions[$last]=${transitions[$last]}','$first','
done

paths=()

find_paths() {
  local current_path=( ${1//,/ } )
  local marked_caves=$2
  local visited_twice=$3
  local current_transitions=${transitions[${current_path[-1]}]}
  current_transitions=( ${current_transitions//,/ } )
  local current_transition
  for current_transition in ${current_transitions[@]}; do
    if [[ $current_transition == 'end' ]]; then
      paths+=( $1','$current_transition',' )
    elif [[ ${current_transition:0:1} == [A-Z] ]]; then
      find_paths $1','$current_transition',' $marked_caves $visited_twice
    elif ! [[ $marked_caves == *','$current_transition','* ]]; then
      find_paths $1','$current_transition',' $marked_caves','$current_transition',' $visited_twice
    elif [ $visited_twice -eq 0 ] && ! [[ $current_transition == 'start' ]]; then
      find_paths $1','$current_transition',' $marked_caves 1
    fi
  done
}

find_paths ',start,' ',start,' 0

echo ${#paths[@]}