Source: Arithmetic Logic Unit

Part 1: Simulate an ALU with 4 registers (w, x, y, and z) and instructions defined below. Find the largest 14 digit number with no 0 digits which result in z=0.

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Source: Amphipod

Part 1: Given 4 rooms full of amphipods with various energy costs for movement (a=1, b=10, c=100, d=1000) and a hallway, how much energy does it take (at minimum) to sort the amphipods into their own rooms with the following conditions:

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Source: Reactor Reboot

Part 1: Given a series of 3D cubes that either turn ON all or turn OFF all points in their region, calculate how many points in the region (-50..50,-50..50,-50..50) are ON at the end.

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Source: Dirac Dice

Part 1: Play a simple game (describe below) with a loaded D100 (that always rolls 1, 2, 3, … 99, 100, 1, …). Return the score of the losing player times the number of times the die was rolled.

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Source: Chiton

Part 1: Given a grid of weights, find the minimum path from top left to top right. Return the total weight along that path.

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Source: Passage Pathing

Part 1: Given a list of edges in a bi-directional graph, count the number of paths from start to end such that nodes named with lowercase letters are visited once, and nodes with uppercase letters can be visited any number of times.

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Source: Duet

Part 1: Create a virtual machine with the following instruction set:

• snd X plays a sound with a frequency equal to the value of X
• set X Y sets register X to Y
• add X Y set register X to X + Y
• mul X Y sets register X to X * Y
• mod X Y sets register X to X mod Y
• rcv X recovers the frequency of the last sound played, if X is not zero
• jgz X Y jumps with an offset of the value of Y, iff X is greater than zero

In most cases, X and Y can be either an integer value or a register.

What is the value recovered by rcv the first time X is non-zero?

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Source: Spinlock¹

Part 1: Start with a circular buffer containing [0] and current_position = 0. For n from 1 up to 2017:

1. Step forward steps (puzzle input)
2. Input the next value for n, set current_position to n, increment n
3. Repeat

What is the value after 2017?

It’s a bit weird to describe, but the given example helps (assume steps = 3):

(0)
0 (1)
0 (2) 1
0  2 (3) 1
0  2 (4) 3  1
0 (5) 2  4  3  1
0  5  2  4  3 (6) 1
0  5 (7) 2  4  3  6  1
0  5  7  2  4  3 (8) 6  1
0 (9) 5  7  2  4  3  8  6  1

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Source: Permutation Promenade

Part 1: Running on the string a...p apply a series of the following commands:

• sX rotates the string right by X positions
• xX/Y swaps positions X and Y
• pA/B swaps the letters A and B no matter their positions

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Source: Radioisotope Thermoelectric Generators

Part 1: Input will be a list of the following form:

• The first floor contains a hydrogen-compatible microchip and a lithium-compatible microchip.
• The second floor contains a hydrogen generator.
• The third floor contains a lithium generator.
• The fourth floor contains nothing relevant.

You have an elevator that can move exactly 1 or 2 items. You can only leave a microchip on a floor with a non-matching generator if a matching generator is also present.

Move all items to the top (4th) floor.

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