Source: Day 21: Keypad Conundrum

Full solution for today (spoilers!).

Part 1

You are trying to type a code on a keypad:

+---+---+---+
| 7 | 8 | 9 |
+---+---+---+
| 4 | 5 | 6 |
+---+---+---+
| 1 | 2 | 3 |
+---+---+---+
    | 0 | A |
    +---+---+

But you cannot type directly. Instead, you can control a pointer on the keypad with arrow keys:

    +---+---+
    | ^ | A |
+---+---+---+
| < | v | > |
+---+---+---+

Whenever you type a ^ on the arrow keys, the pointer on the keypad will move up one, etc. When you type A, then the pointer on the keypad will type whatever it is pointing at.

But that’s not enough either. Add a second keypad. And then a third, that is the one you are actually controlling.

For each output sequence multiple the length of the minimum input sequence needed to generate it by the numeric value of the input sequence (ignoring any A); sum these.

Note: Moving off any keypad or into the blank spaces is an error.

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Source: Day 20: Race Condition

Full solution for today (spoilers!).

Part 1

Given a maze with exactly one path, find how many single walls you can walk through (remove) that shorten the best path by at least 100 units.

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Source: Day 19: Linen Layout

Full solution for today (spoilers!).

Part 1

Given a comma delimited list of substrings and a list of strings, count how many of the latter strings can be made up of any (repeating) combination of the former.

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Source: Day 18: RAM Run

Full solution for today (spoilers!).

Part 1

You are given a series of points on a 71x71 grid. Taking only the first 1024 points, how long is the shortest path from (0, 0) to (70, 70)?

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Source: Day 17: Chronospatial Computer

Full solution for today (spoilers!).

Part 1

Implement a virtual machine. The machine will have 3 unbounded signed registers, 8 opcodes (see below), a variable parameter scheme (see below that). You will be given the initial values of the 3 registers and a program. Find the final output.

Instructions

Parameter specification

For instructions that can take reg/val, 0 to 3 (inclusive) are treated as literal values, 4 is register A, 5 is B, 6, is C, and 7 is an error (should never happen).

For instructions that only take val, it’s always a literal value in the range 0 to 7 (inclusive).

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Source: Day 16: Reindeer Maze

Full solution for today (spoilers!).

Part 1

Given a maze, what is the shortest path between S and E where walking straight costs one and turning costs 1000.

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Source: Day 15: Warehouse Woes

Full solution for today (spoilers!).

Part 1

Given a warehouse containing floors (.), walls (#), boxes (O), and the player (@) plus a series of instructions ^V<>, move the player according to the instructions, pushing boxes (which in turn can push more boxes).

Calculate the sum of y * 100 + x for each box’s final position.

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Source: Day 14: Restroom Redoubt

Full solution for today (spoilers!).

Part 1

Given a series of robots defined with initial position and velocity on a 101x103 toroidal grid, calculate where the robots will be after 100 iterations. Return the product of the number of robots in each quadrant of the final grid, ignoring the middle lines (since they’re odd).

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Source: Day 13: Claw Contraption

Full solution for today (spoilers!).

Part 1

Given Button A (ax, ay), Button B (bx, by), and Prize (px, py); how many times must you press Button A (a) and Button B (b) to reach the Prize? Sum 3a + b for each machine that has a solution.

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Source: Day 12: Garden Groups

Full solution for today (spoilers!).

Part 1

Given a Grid of regions, calculate the sum of the product perimeter * area for each region.

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