# --- Day 6: Custom Customs ---
#
# As your flight approaches the regional airport where you'll switch to a much
# larger plane, customs declaration forms are distributed to the passengers.
#
# The form asks a series of 26 yes-or-no questions marked a through z. All you
# need to do is identify the questions for which anyone in your group answers
# "yes". Since your group is just you, this doesn't take very long.
#
# However, the person sitting next to you seems to be experiencing a language
#  barrier and asks if you can help. For each of the people in their group, you
#  write down the questions for which they answer "yes", one per line. For example:
#
# abcx
# abcy
# abcz
#
# In this group, there are 6 questions to which anyone answered
# "yes": a, b, c, x, y, and z. (Duplicate answers to the same question don't
# count extra; each question counts at most once.)
#
# Another group asks for your help, then another, and eventually you've collected
# answers from every group on the plane (your puzzle input). Each group's answers
# are separated by a blank line, and within each group, each person's answers are
# on a single line. For example:
#
# abc
#
# a
# b
# c
#
# ab
# ac
#
# a
# a
# a
# a
#
# b
#
# This list represents answers from five groups:
#
# The first group contains one person who answered "yes" to 3 questions: a, b, and c.
# The second group contains three people; combined, they answered "yes" to 3 questions: a, b, and c.
# The third group contains two people; combined, they answered "yes" to 3 questions: a, b, and c.
# The fourth group contains four people; combined, they answered "yes" to only 1 question, a.
# The last group contains one person who answered "yes" to only 1 question, b.
#
# In this example, the sum of these counts is 3 + 3 + 3 + 1 + 1 = 11.
#
# For each group, count the number of questions to which anyone answered "yes".
# What is the sum of those counts?

library(stringi)
library(magrittr)
library(tidyverse)

# input <- readLines("/tmp/test.txt")
input <- readLines("../input/06-01.txt", warn = FALSE)

# 04-01 -------------------------------------------------------------------

split(input, findInterval(1:length(input), which(input == ""))) %>%
  map_int(~length(unique(unlist(strsplit(.x, ""))))) %>%
  sum()

# --- Part Two ---
#
# As you finish the last group's customs declaration, you notice that you misread
# one word in the instructions:
#
# You don't need to identify the questions to which anyone answered "yes"; you
# need to identify the questions to which everyone answered "yes"!
#
# Using the same example as above:
#
# abc
#
# a
# b
# c
#
# ab
# ac
#
# a
# a
# a
# a
#
# b
# This list represents answers from five groups:
#
# In the first group, everyone (all 1 person) answered "yes" to 3 questions: a, b, and c.
# In the second group, there is no question to which everyone answered "yes".
# In the third group, everyone answered yes to only 1 question, a. Since some
#   people did not answer "yes" to b or c, they don't count.
# In the fourth group, everyone answered yes to only 1 question, a.
# In the fifth group, everyone (all 1 person) answered "yes" to 1 question, b.
#
# In this example, the sum of these counts is 3 + 0 + 1 + 1 + 1 = 6.
#
# For each group, count the number of questions to which everyone answered "yes".
# What is the sum of those counts?
#

# 04-02

split(input, findInterval(1:length(input), which(input == ""))) %>%
  map(discard, equals, "") %>%
  map_int(~{
    sum(table(unlist(strsplit(.x, ""))) == length(.x))
  }) %>%
  sum()