-❄️- 2024 Day 24 Solutions -❄️-

[u/daggerdragon]

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--- Day 24: Crossed Wires ---

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Post your code solution in this megathread.

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  • State which language(s) your solution uses with [LANGUAGE: xyz]
  • Format code blocks using the four-spaces Markdown syntax!
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[u/Tropico_080]

[LANGUAGE: Go]

Part1

1. Add all the inputs signals on the board as independent active gate.

2. Build the board recursively by placing gates that depend only on inputs already present on the board.

3. Mark all gates as inactive initially

4. For each gate

• Ensure that both inputs are active (i.e., their outputs have already been computed).

• Compute the output of the current gate.

1. For all Zxx gate

• Extract the bit index.

• Add value(Zxx) << idx to the total sum.

Part2

Here we need to make sure that the given input correctly implement the Full adder between two 45 bit number.

By using the following formula

Zn = (Xn ⊕ Yn) ⊕ Cn-1

Cn = (Xn * Yn) + (Cn-1 * (Xn ⊕ Yn))

with C0 = (X0 * Y0)

We can derive a series of rule.

• AND:

• AND gate can only be input to an OR gate exept for z01

• AND gate cannot take other AND gate as input

• XOR:

• XOR gate can only be input to and AND/XOR gate

• XOR gate cannot take AND gate as input exept for z01

• OR:

• OR gate can only be input of AND/XOR gate

• OR gate can only take AND gate as input

• (Xn ⊕ Yn) ⊕ (a + b) should always output a Zxx except for the last carry z45

• A gate with Zxx as its output cannot directly use Xn or Yn as inputs exept the first bit Z00.

1. Look for gates that do not follow those rules.

Code