day18.py

#!/usr/bin/env python3

import regex as re

bg = re.compile(r"\([^)(]*+(?:(?R)[^)(]*)*+\)", re.VERSION1)

src = open("input.txt", "r").readlines()

src2 = """
1 + 2 * 3 + 4 * 5 + 6
1 + (2 * 3) + (4 * (5 + 6))
2 * 3 + (4 * 5)
5 + (8 * 3 + 9 + 3 * 4 * 3)
5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))
((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2
""".splitlines()

src = [r.strip() for r in src if r.strip()]


def tokenize(line):
    out = []
    for c in line.split(" "):
        if c.isdigit():
            out.append(int(c))
        elif c in "+*()":
            out.append(c)
    return out


def solve(eq):
    for m in bg.finditer(eq):
        g = m.group()
        eq = eq.replace(g, solve(g[1:-1]))

    eq = tokenize(eq)

    while "+" in eq:
        p = eq.index("+")
        v = eq[p - 1] + eq[p + 1]
        eq = eq[0 : p - 1] + [v] + eq[p + 2 :]

    while len(eq) != 1:
        l, op, r = eq.pop(0), eq.pop(0), eq.pop(0)

        if op == "+":
            eq.insert(0, l + r)
        else:
            eq.insert(0, l * r)

    return str(eq.pop())


s = 0
for line in src:
    s += int(solve(line))

print(s)