AOC2021Day14.py

template = ''
pairRules = {}

def getPuzzleData():
    template = ''
    pairRules = {}

    with open('AOC2021D14.txt') as INFILE:
        lines = INFILE.read().split('\n')

    template = lines[0]

    for line in range(2, len(lines)):
        lineElems = lines[line].split(' -> ')
        pairRules[lineElems[0]] = lineElems[1]

    return template, pairRules


def doStep(aTemplate, aPairRules):
    lTemplate = ''
    lOldPairs = []
    lNewPairs = []

    for pairStartPos in range(len(aTemplate) - 1):
        lOldPairs.append(aTemplate[pairStartPos:pairStartPos+2])

    for lOldPair in lOldPairs:
        if lOldPair in aPairRules:
            lNewPairs.append(lOldPair[0] + aPairRules[lOldPair] + lOldPair[1])

    lTemplate = lNewPairs[0]

    for lNewPairIdx in range(1, len(lNewPairs)):
        if lTemplate[-1] == lNewPairs[lNewPairIdx][0]:
            lTemplate += lNewPairs[lNewPairIdx][1:]
        else:
            lTemplate += lNewPairs[lNewPairIdx]


    return lTemplate

def getElementQuantities(aTemplate):
    lElementQuantitites = {}

    for element in aTemplate:
        lElementQuantitites.setdefault(element, 0)
        lElementQuantitites[element] += 1

    lElementQuantitites = sorted(lElementQuantitites.items(), key=lambda item: item[1])
    return lElementQuantitites

#
# Main program
#

STEPS=10
template, pairRules = getPuzzleData()
print(f'{template=}')
print(f'{pairRules=}')

for step, _ in enumerate(range(STEPS), start=1):
    template = doStep(template, pairRules)
    print(f'After {step=}: {len(template)=}')

elementQuantities = getElementQuantities(template)
print(f'{elementQuantities}')
print(f'{elementQuantities[0][1]}')
print(f'{elementQuantities[-1][1] - elementQuantities[0][1]}')