Given a grid of costs, find the shortest path from top left to bottom right. You may not double back or go straight more than 3 steps in a row.

You are given a grid of mirrors (|-\/) and empty space (.).

Diagonal mirrors just relect the light.

The horizontal and vertical mirrors are splitters, light hitting them head on (like >|) will split to go both directions. Light hitting edge on will just go through it.

Starting in the top left going East, how many total tiles will a light beam illuminate?

Hash each input (comma separated) with h(v, c) = (v + c) * 17 (modulo 256 / as a byte). Sum these values.

Given a grid of # and O (among empty . points) where O can move, slide each O as far north as it can. Score each based on how far north it is.

You are given a grid of . and #. Find the (single) axis of reflection (between two rows or columns).

Given a sequence of #.? as on, off, and unknown and a sequence of group sizes, determine how many possible arrangements there are that match the given groups.

More specifically, if you have ???.## 1,2 you need a single # and a set of two ##, there are three possibilities: #...###, .#..###, and ..#.###.

Read a grid of # (stars) and . (empty space). For each completely empty line or row, add another. Calculate the sum of the Manhattan distances between all pairs of stars.

You are given as input an ASCII art pipe diagram with straight pipes |-, right angle turns LJ7F, ground ., and a start tile S.

The start tile will be part of a loop of pipes.

Find the distance to the furthest connected pipe segment from S (or half the length of the loop).

Given a list of terms, repeatedly calculate the differences of terms until these differences are 0. So:

0   3   6   9  12  15
  3   3   3   3   3
    0   0   0   0

Calculate the sum of next terms for each sequence (18 for this one).

Given a (repeated) sequence of moves (L for left and R for right) and a directed graph where each node has two neighbors (left and right), count how many total steps it takes to get from the node AAA to the node ZZZ. The sequence of moves can (and will) need to repeat.