adventofcode2022/day21/sol.py

import operator

lines = []
for line in open("input"):
    lines.append(line.split())


unused = lines
scope = {}
while unused:
    lines, unused = unused, []
    for words in lines:
        refs = [x for x in words[1:] if x.isalpha()]
        if any(r not in scope for r in refs):
            unused.append(words)
            continue
        dst = words[0].rstrip(':')
        if len(words) == 2:
            _, src = words
            scope[dst] = int(src)
            continue
        _, x, op, y = words
        scope[dst] = (op, scope[x], scope[y])

optab = {
    '*': operator.mul,
    '/': operator.floordiv,
    '+': operator.add,
    '-': operator.sub,
}

def eval(x):
    if type(x) == int:
        return x
    op = x[0]
    args = [eval(a) for a in x[1:]]
    return optab[op](*args)

root = scope['root']
print(eval(root))

def solve(x):
    _, left, right = x

    humn = scope['humn']
    path = set()

    def find(x):
        if x is humn:
            path.add(x)
            return True
        if type(x) is tuple:
            for a in x:
                if find(a):
                    path.add(x)
                    return True
            else:
                return False
        return False

    x, y = left, right
    if not find(x):
        find(y)
        x, y = y, x

    #print(x)
    assert x in path
    y = eval(y)

    while x is not humn:
        assert len(x) == 3
        op, a, b = x
        if op == '/':
            if a in path:
                y = ('*', y, b)
            else:
                raise ValueError("ruh-roh")
        elif op == '*':
            if a in path:
                y = ('/', y, b)
            else:
                y = ('/', y, a)
        elif op == '+':
            if a in path:
                y = ('-', y, b)
            else:
                y = ('-', y, a)
        elif op == '-':
            if a in path:
                # x - b = y => x = y + b
                y = ('+', y, b)
            else:
                # a - x = y  => x = a - y
                y = ('-', a, y)
        else:
            raise ValueError("unknown op "+repr(op))
        if a in path:
            x = a
        else:
            x = b
    return eval(y)

print(solve(root))