03.py

# --- Day 3: Rucksack Reorganization ---
#
# One Elf has the important job of loading all of the rucksacks with
# supplies for the jungle journey.  Unfortunately, that Elf didn't
# quite follow the packing instructions, and so a few items now need
# to be rearranged.
#
# Each rucksack has two large compartments.  All items of a given type
# are meant to go into exactly one of the two compartments.  The Elf
# that did the packing failed to follow this rule for exactly one item
# type per rucksack.
#
# The Elves have made a list of all of the items currently in each
# rucksack (your puzzle input), but they need your help finding the
# errors.  Every item type is identified by a single lowercase or
# uppercase letter (that is, a and A refer to different types of
# items).
#
# The list of items for each rucksack is given as characters all on a
# single line.  A given rucksack always has the same number of items
# in each of its two compartments, so the first half of the characters
# represent items in the first compartment, while the second half of
# the characters represent items in the second compartment.
#
# For example, suppose you have the following list of contents from
# six rucksacks:
#
# vJrwpWtwJgWrhcsFMMfFFhFp
# jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
# PmmdzqPrVvPwwTWBwg
# wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
# ttgJtRGJQctTZtZT
# CrZsJsPPZsGzwwsLwLmpwMDw
#
# - The first rucksack contains the items vJrwpWtwJgWrhcsFMMfFFhFp,
#   which means its first compartment contains the items vJrwpWtwJgWr,
#   while the second compartment contains the items hcsFMMfFFhFp.  The
#   only item type that appears in both compartments is lowercase p.
# - The second rucksack's compartments contain jqHRNqRjqzjGDLGL and
#   rsFMfFZSrLrFZsSL.  The only item type that appears in both
#   compartments is uppercase L.
# - The third rucksack's compartments contain PmmdzqPrV and vPwwTWBwg;
#   the only common item type is uppercase P.
# - The fourth rucksack's compartments only share item type v.
# - The fifth rucksack's compartments only share item type t.
# - The sixth rucksack's compartments only share item type s.
#
# To help prioritize item rearrangement, every item type can be
# converted to a priority:
#
# - Lowercase item types a through z have priorities 1 through 26.
# - Uppercase item types A through Z have priorities 27 through 52.
#
# In the above example, the priority of the item type that appears in
# both compartments of each rucksack is 16 (p), 38 (L), 42 (P),
# 22 (v), 20 (t), and 19 (s); the sum of these is 157.
#
# Find the item type that appears in both compartments of each
# rucksack.  What is the sum of the priorities of those item types?

def priority(type):
    return ord(type) - (ord("a")-1 if type.islower() else ord("A")-27)

sacks = open("03.in").read().split()

print(
    sum(
        priority((set(s[:len(s)//2]) & set(s[len(s)//2:])).pop())
        for s in sacks
    )
)

# --- Part Two ---
#
# As you finish identifying the misplaced items, the Elves come to you
# with another issue.
#
# For safety, the Elves are divided into groups of three.  Every Elf
# carries a badge that identifies their group.  For efficiency, within
# each group of three Elves, the badge is the only item type carried
# by all three Elves.  That is, if a group's badge is item type B,
# then all three Elves will have item type B somewhere in their
# rucksack, and at most two of the Elves will be carrying any other
# item type.
#
# The problem is that someone forgot to put this year's updated
# authenticity sticker on the badges.  All of the badges need to be
# pulled out of the rucksacks so the new authenticity stickers can be
# attached.
#
# Additionally, nobody wrote down which item type corresponds to each
# group's badges.  The only way to tell which item type is the right
# one is by finding the one item type that is common between all three
# Elves in each group.
#
# Every set of three lines in your list corresponds to a single group,
# but each group can have a different badge item type.  So, in the
# above example, the first group's rucksacks are the first three
# lines:
#
# vJrwpWtwJgWrhcsFMMfFFhFp
# jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
# PmmdzqPrVvPwwTWBwg
#
# And the second group's rucksacks are the next three lines:
#
# wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
# ttgJtRGJQctTZtZT
# CrZsJsPPZsGzwwsLwLmpwMDw
#
# In the first group, the only item type that appears in all three
# rucksacks is lowercase r; this must be their badges.  In the second
# group, their badge item type must be Z.
#
# Priorities for these items must still be found to organize the
# sticker attachment efforts: here, they are 18 (r) for the first
# group and 52 (Z) for the second group.  The sum of these is 70.
#
# Find the item type that corresponds to the badges of each three-Elf
# group.  What is the sum of the priorities of those item types?

print(
    sum(
        priority((set(sacks[i]) & set(sacks[i+1]) & set(sacks[i+2])).pop())
        for i in range(0, len(sacks), 3)
    )
)