advent-of-code/2024/day-19/solution-2.sh

#!/usr/bin/env bash

TOWEL_FILE=$1
DESIGN_FILE=$2

read -r -a TOWELS <<< "$( < "$TOWEL_FILE" tr ',' ' ' | paste -s -d " " )"
read -r -a DESIGNS <<< "$( < "$DESIGN_FILE" paste -s -d " " )"

# Check if towel is a viable match
match_towel () {
  TOWEL=$1
  MATCH=$2
  FULL_DESIGN=$3

  TO_MATCH="$MATCH$TOWEL"
  PARTIAL_DESIGN=${FULL_DESIGN::${#TO_MATCH}}
  if [[ $PARTIAL_DESIGN == "$TO_MATCH" ]]
  then
    return 0
  else
    return 1
  fi
}

TOTAL_VALID=0
# Loop through designs
for DESIGN in "${DESIGNS[@]}"
do
  # The idea is for each design, keep a sum of combinations
  # for each index position of the DESIGN string
  # Since the branches "multiply", just take the sum
  # at the starting index, and add it to the end 
  # of the "combined" index
  # for each possible combination.
  printf "Starting design : %s\n" "$DESIGN"
  declare -A POINTER_LIST
  POINTER_LIST[0]=1
  POINTER_END=$(( ${#DESIGN}  ))

  while true
  do
    POINTER=${#DESIGN}
    # Pick lowest pointer value
    for P in "${!POINTER_LIST[@]}"
    do
      if [[ $P -lt $POINTER ]] 
      then
        POINTER=$P
      fi
    done
    POINTER_VALUE=${POINTER_LIST[$POINTER]}
    # Check if end has reached
    if [[ $POINTER -eq $POINTER_END ]]
    then
      break
    fi

    # Loop through towels and remove earliest pointer
    for TOWEL in "${TOWELS[@]}"
    do
      TOWEL_LEN=${#TOWEL}
      END=$(( POINTER + TOWEL_LEN ))
      if [[ ${DESIGN:$POINTER:$TOWEL_LEN} == "$TOWEL" ]]
      then
	POINTER_LIST[$END]=$(( ${POINTER_LIST[$END]} + POINTER_VALUE ))
      fi
    done

    # Done looping through for specific point
    unset "POINTER_LIST[$POINTER]" 
  done
  printf "Total matches for %s is %s.\n" "$DESIGN" "${POINTER_LIST[$POINTER_END]}"
  TOTAL_VALID=$(( TOTAL_VALID + POINTER_LIST[$POINTER_END] ))
  unset "POINTER_LIST"
done
printf "Total valid designs: %s\n" "$TOTAL_VALID"