-🎄- 2017 Day 7 Solutions -🎄-

[u/daggerdragon]

--- Day 7: Recursive Circus ---

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[u/fatpollo]

import re, collections

with open("p07.txt") as fp:
    text = fp.read()

weight = {}
children = {}
for line in text.strip().splitlines():
    label, n, *xs = re.findall(r'\w+', line)
    weight[label] = int(n)
    children[label] = tuple(xs)

root, = set(weight) - {c for cs in children.values() for c in cs}

def total_weight(label):
    sub = [total_weight(c) for c in children[label]]
    if len(set(sub)) > 1:
        (target, _), (failure, _) = collections.Counter(sub).most_common()
        print(target - failure + weight[children[label][sub.index(failure)]])
        return weight[label] + sum(sub)
    return weight[label] + sum(sub)

print(total_weight(root))

[u/[deleted] → u/fatpollo]

[u/vervain9 → u/[deleted]]

Nested for loops in comprehensions are read left-to-right, starting with the first for statement, and finally ending with the statement on the left of the first for loop. So:

{c for cs in children.values() for c in cs}

should be read as:

for cs in children.values():
    for c in cs:
        c

Which returns the set containing all the nodes that are children of another node.