#!/usr/bin/env python3

from pprint import pprint

with open('input.txt', 'r') as f:
    polymer = f.read()

print('Polymer length:', len(polymer))

def reacts(el_1, el_2):
    return el_1 != el_2 and el_1.upper() == el_2.upper()

def reduce_polymer_naive(polymer):
    """Faster but not correct solution. Can be used for first reduction of data
    """
    poly = list(polymer)

    i = 0
    gap = 1
    while i < len(poly):
        if i < 0 or i + gap >= len(poly):
            i += gap
            gap = 1
            continue
        
        el = poly[i]
        next_el = poly[i + gap]
        if reacts(el, next_el):
            poly[i] = '-'
            poly[i + gap] = '-'
            i -= 1
            gap += 2
            continue

        i += gap
        gap = 1
    return ''.join([el for el in poly if el != '-'])

def reduce_polymer(polymer):
    polymer = reduce_polymer_naive(polymer)
    modifications = True
    rounds = 0
    while modifications:
        modifications = False
        rounds += 1
        mods = 0

        new_polymer = []
        skip = False
        for i, el in enumerate(polymer[:-1]):
            if skip:
                skip = False
                continue
            next_el = polymer[i + 1]
            if el != next_el and el.upper() == next_el.upper():
                modifications = True
                mods += 1
                skip = True
                continue

            new_polymer.append(el[-1])

        if not skip:
            new_polymer.append(polymer[-1])

        polymer = ''.join(new_polymer)
    return polymer


alphabet = 'abcdefghijklmnopqrstuvwxyz'

count_dict = dict()

for el in alphabet:
    new_poly = ''.join([x for x in polymer if x not in (el, el.upper())])
    count_dict[el] = len(reduce_polymer(new_poly))
    print(f'Processed {el}, len: {count_dict[el]}')

pprint(count_dict)
min_idx = min(count_dict, key=count_dict.get)
print(min_idx, count_dict[min_idx])