Add problems for days 1-7

2020/day02/problem

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+# Advent of Code
+
+--- Day 2: Password Philosophy ---
+
+   Your flight departs in a few days from the coastal airport; the easiest way down to the
+   coast from here is via toboggan.
+
+   The shopkeeper at the North Pole Toboggan Rental Shop is having a bad day. "Something's
+   wrong with our computers; we can't log in!" You ask if you can take a look.
+
+   Their password database seems to be a little corrupted: some of the passwords wouldn't have
+   been allowed by the Official Toboggan Corporate Policy that was in effect when they were
+   chosen.
+
+   To try to debug the problem, they have created a list (your puzzle input) of passwords
+   (according to the corrupted database) and the corporate policy when that password was set.
+
+   For example, suppose you have the following list:
+
+ 1-3 a: abcde
+ 1-3 b: cdefg
+ 2-9 c: ccccccccc
+
+   Each line gives the password policy and then the password. The password policy indicates
+   the lowest and highest number of times a given letter must appear for the password to be
+   valid. For example, 1-3 a means that the password must contain a at least 1 time and at
+   most 3 times.
+
+   In the above example, 2 passwords are valid. The middle password, cdefg, is not; it
+   contains no instances of b, but needs at least 1. The first and third passwords are valid:
+   they contain one a or nine c, both within the limits of their respective policies.
+
+   How many passwords are valid according to their policies?
+
+   Your puzzle answer was 636.
+
+--- Part Two ---
+
+   While it appears you validated the passwords correctly, they don't seem to be what the
+   Official Toboggan Corporate Authentication System is expecting.
+
+   The shopkeeper suddenly realizes that he just accidentally explained the password policy
+   rules from his old job at the sled rental place down the street! The Official Toboggan
+   Corporate Policy actually works a little differently.
+
+   Each policy actually describes two positions in the password, where 1 means the first
+   character, 2 means the second character, and so on. (Be careful; Toboggan Corporate
+   Policies have no concept of "index zero"!) Exactly one of these positions must contain the
+   given letter. Other occurrences of the letter are irrelevant for the purposes of policy
+   enforcement.
+
+   Given the same example list from above:
+
+     • 1-3 a: abcde is valid: position 1 contains a and position 3 does not.
+     • 1-3 b: cdefg is invalid: neither position 1 nor position 3 contains b.
+     • 2-9 c: ccccccccc is invalid: both position 2 and position 9 contain c.
+
+   How many passwords are valid according to the new interpretation of the policies?
+
+   Your puzzle answer was 588.
+
+   Both parts of this puzzle are complete! They provide two gold stars: **
+
+   At this point, you should return to your Advent calendar and try another puzzle.
+
+   If you still want to see it, you can get your puzzle input.
+
+References
+
+   Visible links
+   . https://adventofcode.com/
+   . https://adventofcode.com/2020/about
+   . https://adventofcode.com/2020/events
+   . https://adventofcode.com/2020/settings
+   . https://adventofcode.com/2020/auth/logout
+   . Advent of Code Supporter
+	https://adventofcode.com/2020/support
+   . https://adventofcode.com/2020
+   . https://adventofcode.com/2020
+   . https://adventofcode.com/2020/support
+   . https://adventofcode.com/2020/sponsors
+   . https://adventofcode.com/2020/leaderboard
+   . https://adventofcode.com/2020/stats
+   . https://adventofcode.com/2020/sponsors
+   . https://en.wikipedia.org/wiki/Toboggan
+   . https://adventofcode.com/2020
+   . https://adventofcode.com/2020/day/2/input