№12 — #1214

import re
def strip_html(s):
    s = re.sub(r'<sub>(\d+)</sub>', r'\1', s)
    s = re.sub(r'<[^>]+>', '', s)
    return s.strip()
def simulate_tm(full_html, tape_list, head_pos, init_state='q0'):
    rows = re.findall(r'<tr[^>]*>(.*?)</tr>', full_html, re.DOTALL)
    hdr = re.findall(r'<th[^>]*>(.*?)</th>|<td[^>]*>(.*?)</td>', rows[0], re.DOTALL)
    symbols = [strip_html(c[0] or c[1]) for c in hdr[1:]]
    trans = {}
    for row in rows[1:]:
        cells = re.findall(r'<th[^>]*>(.*?)</th>|<td[^>]*>(.*?)</td>', row, re.DOTALL)
        if not cells: continue
        state = strip_html(cells[0][0] or cells[0][1]).replace(' ', '')
        trans.setdefault(state, {})
        for i, cell in enumerate(cells[1:]):
            if i >= len(symbols): break
            sym = symbols[i]
            cmd = strip_html(cell[0] or cell[1])
            if not cmd: continue
            parts = [p.strip() for p in cmd.split(',')]
            if len(parts) == 3:
                trans[state][sym] = (parts[0], parts[1], parts[2].replace(' ', ''))
    tape = list(tape_list)
    pos = head_pos
    state = init_state
    for _ in range(500000):
        while pos < 0: tape.insert(0, 'λ'); pos += 1
        while pos >= len(tape): tape.append('λ')
        sym = tape[pos]
        if state not in trans or sym not in trans[state]: break
        w, d, ns = trans[state][sym]
        tape[pos] = w
        if d == 'S': state = ns; break
        elif d == 'L': pos -= 1
        elif d == 'R': pos += 1
        state = ns
    return tape, pos, state
# Головка у левого λ. Результат = 4087. Найти исходное число N.
# 4087 = 111111110111₂ = '1' + '11111110' + '111'
# Алгоритм: '1' + копия_битов + '111'
# Из 4087 = '1' + N_bits + '111': N_bits = '11111110' → N = 254
import json
with open(__file__.replace('.py','') + '/../products/fixtures/tasks.json') as f:
    tasks = json.load(f)
t = next(x for x in tasks if x['pk'] == 5479)
full = t['fields']['statement'] + t['fields']['statement2']
tables = re.findall(r'<table[^>]*>.*?</table>', full, re.DOTALL)
table_html = tables[-1]
N = 254
tape = ['λ'] + list(bin(N)[2:]) + ['λ']
head = 0
result, rpos, rstate = simulate_tm(table_html, tape, head)
bits = ''.join(c for c in result if c != 'λ')
assert int(bits, 2) == 4087
print(N)
# Ответ: 254