AoC 2016 Day 6: Signal Unjammer

2016-12-06

Source: Signals and Noise

Part 1: Given a list of strings, find the most common character in each position.

AoC 2016 Day 5: Password Cracker

2016-12-05

Source: How About a Nice Game of Chess?

Part 1: Generate a series of hashes: MD5(salt + index). For each hash starting with five zeros, write down the sixth character.

AoC 2016 Day 4: Room Validator

2016-12-04

Source: Security Through Obscurity¹

Part 1: A room is described as a name, a sector ID, and a checksum as follows:

aaaaa-bbb-z-y-x-123[abxyz]

name: aaaaa-bbb-z-y-x sector ID: 123 checksum: abxyz


> A room is valid if the checksum contains the five most common letters if the name (ties broken alphabetically).





An interesting problem. The first thing that we have to do is parse the input:

```python
with open(args.input_file, 'r') as fin:
    for room in fin:
        m = re.match(r'([a-z-]+)-(\d+)\[([a-z]+)\]', room)
        name, sector_id, checksum = m.groups()

        ...

The next thing we want to do is generate a checksum (so we can see if it’s correct):

AoC 2016 Day 3: Triangle Validator

2016-12-03

Source: Squares With Three Sides

Part 1: Given a list of sides, determine how many form valid triangles. (Hint: triangle inequality)

AoC 2016 Day 2: Pin Typer

2016-12-02

Source: Bathroom Security

Part 1: Take a keypad with the following layout:

1 2 3 4 5 6 7 8 9


> Using the instructions UDLR for Up, Down, Left, and Right respectively, move a 'finger' around over the keypad. At the end of each line of instructions, output the current digit.





First, let's define the grid. We'll use the same trick with complex numbers as [last time]https://blog.jverkamp.com/2016/12/01/aoc-2016-day-1-taxicab-simulator/.

```python
grid = {
    '-1-1j': 1, '+0-1j': 2, '+1-1j': 3,
    '-1+0j': 4, '+0+0j': 5, '+1+0j': 6,
    '-1+1j': 7, '+0+1j': 8, '+1+1j': 9,
}

From there, we can move around the grid, make sure we don’t move off the end, and output a character at the end of each line: