# AoC 2018 Day 12: Fat Cellular Automaton

### Source: Subterranean Sustainability

Part 1: Create an infinite 2D cellular automaton with transition rules based on two points to each side, starting with initial state at index 0 to the right.

After 20 generations, what is the sum of indexes of points turned on?

# AoC 2018 Day 11: Gridlocked Fuel

### Source: Chronal Charge

Part 1: Define a grid as follows (x,y coordinates + a constant C):

• r(x) = x + 10
• G(x, y) = hundreds(r(x) * (r(x) * y + C)) - 5

Find the 3x3 area in a 300x300 grid with the highest total G(x, y) .

# AoC 2018 Day 10: It's Full of Stars!

### Source: The Stars Align

Part 1: Given a system of moving particles (with position and velocity) find the point where the particles spell a message. What is that message?

# AoC 2018 Day 9: Marble Madness

### Source: Marble Mania

Part 1: Place marbles in a circle such that each marble is placed by skipping one place except for marbles divisible by 23. For those, don’t place them, skip back 7 places, and remove that marble as well. Add these two marbles to your current score.

Given a specific player count and last marble, what’s the highest score?

# AoC 2018 Day 8: Checksum Treeification

### Source: The Sum of Its Parts

Part 1: A custom tree data structure is defined as:

• child count
• metadata count
• child count additional subtrees (recursive)
• metadata count metadata nodes

Calculate the sum of all metadata nodes.

# AoC 2018 Day 7: Job Simulator

### Source: The Sum of Its Parts

Part 1: Given a list of job dependencies (job A must be before job B), determine the order jobs must be done in. Break ties lexicographically.

# AoC 2018 Day 6: Infinite Area Simulator

### Source: Chronal Coordinates

Part 1: Given a list of points, calculate the region of points closest to each point (using Manhattan distance). Return the size of the largest non-infinite region.

# AoC 2018 Day 5: Alchemical reduction

### Source: Alchemical Reduction

Part 1: Given a string, reduce it by removing pairs of letters that are the same letter but different cases. Repeat until you have a minimal string.

# AoC 2018 Day 4: Sleeping on the job

### Source: Repose Record

Part 1: Given a log of guard shifts and times asleep/awake, calculate the guard that was asleep most often and which minute they were most asleep for.

# AoC 2018 Day 3: Regionification

### Source: No Matter How You Slice It

Part 1: Given a list of overlapping regions defined by (left, top, width, height) count how many integer points occur in more than one region.