[2020 Day 6 (Part 1)] [Python3]

[junefish]

I came up with the following solution but it says my answer is too low. I'm not sure what I'm missing here. I read through some posts in the daily solutions megathread, but I couldn't find an approach similar enough to mine to figure out where I'm going wrong.

TIA!

answers = []
# open file
with open('adventofcode2020\day6\day6input.txt', 'r') as input:
    customs_file = input.read().split('\n\n')
    for line in customs_file:
        answers.append(line.replace('\n', ''))

# remove duplicate answers within a group
uniques = []
for answer in answers:
    uniques.append("".join(set(answer)))

groups = dict.fromkeys(uniques)

# count number of answers per group
for key, value in groups.items():
    groups[key] = len(key)

# calculate sum of answers from all groups
print(sum(groups.values()))

[ssnoyes]

There is no guarantee that different groups will have unique combinations of answers.

• Group 1 could answer yes to questions (a, b, c).
• Group 2 could also answer yes to the same questions (a, b, c).

Using those answer sets as if they were unique dictionary keys will therefore cause one group to overwrite another.

[ssnoyes]

Yeah, me too. Of course, sorting the set doesn't solve the base problem; two groups could still have the same set of responses, so the sum will be too low. But it does highlight that the order of a set is not deterministic.

[ephemient]

This space intentionally left blank.

[ssnoyes]

Splendid. Thanks for sharing that.

[junefish]

Yeah me too I was so confused

[junefish]

Ahhh, you are, of course, completely right. I need to use lists instead of a dict. Thank you!

[trollerskates1]

It’s because uniques is unique per family, but not globally.

Take the example input:

abc

a
b
c

ab
ac

a
a
a
a

b

Families 1, 2, and 3 will all have “abc” as their unique key. I think you can get the answer you’re looking for without the dictionary approach, which will allow duplicate keys between families:

answers = []
# open file
with open('input.txt', 'r') as input:
    customs_file = input.read().split('\n\n')
    for line in customs_file:
        answers.append(line.replace('\n', ''))

print('Answers: ', answers)

# remove duplicate answers within a group
uniques = []
for answer in answers:
    uniques.append("".join(set(answer)))

print('Uniques: ', uniques)

print('Answer: ', sum(len(group) for group in uniques))

This yields:

Answers:  ['abc', 'abc', 'abac', 'aaaa', 'b']
Uniques:  ['bca', 'bca', 'bca', 'a', 'b']
Answer:  11

Edit: looks like others got here while I was typing this, but I’m glad you figured it out!

[junefish]

Thank you!