day9.py

import sys
import re


def decompress(s):
    d = []
    while True:
        m = re.search('(\((\d+)x(\d+)\)).*', s)
        if m:
            n_chars, mult = map(int, m.groups()[1:])
            start, end = m.span(1)
            d.append(s[:start])
            r = s[end:][:n_chars] * mult
            d.append(r)
            s = s[(end + n_chars):]
        else:
            d.append(s)
            break
    return ''.join(d)

def decompress2(s):

    def f(s):
        n = 0
        while s:
            m = re.search('(\((\d+)x(\d+)\)).*', s)
            if m:
                n_chars, mult = map(int, m.groups()[1:])
                start, end = m.span(1)
                n += start + (f(s[end:][:n_chars]) * mult)
                s = s[(end + n_chars):]
            else:
                n += len(s)
                s = s[len(s):]
        return n

    return f(s)

assert len(decompress('ADVENT')) == 6
assert len(decompress('A(1x5)BC')) == 7
assert len(decompress('(3x3)XYZ')) == 9
assert len(decompress('A(2x2)BCD(2x2)EFG')) == 11
assert len(decompress('(6x1)(1x3)A')) == 6
assert len(decompress('X(8x2)(3x3)ABCY')) == 18

print(len(decompress(open('data/day9.txt').read().strip())))

assert decompress2('(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN') == 445
assert decompress2('(3x3)XYZ') == len('XYZXYZXYZ')
assert decompress2('X(8x2)(3x3)ABCY') == len('XABCABCABCABCABCABCY')
assert decompress2('(27x12)(20x12)(13x14)(7x10)(1x12)A') == 241920

print(decompress2(open('data/day9.txt').read().strip()))