71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
## \-\-- Day 7: Some Assembly Required \-\--
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This year, Santa brought little Bobby Tables a set of wires and [bitwise
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logic gates](https://en.wikipedia.org/wiki/Bitwise_operation)!
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Unfortunately, little Bobby is a little under the recommended age range,
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and he needs help [assembling the
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circuit]{title="You had one of these as a kid, right?"}.
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Each wire has an identifier (some lowercase letters) and can carry a
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[16-bit](https://en.wikipedia.org/wiki/16-bit) signal (a number from `0`
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to `65535`). A signal is provided to each wire by a gate, another wire,
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or some specific value. Each wire can only get a signal from one source,
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but can provide its signal to multiple destinations. A gate provides no
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signal until all of its inputs have a signal.
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The included instructions booklet describes how to connect the parts
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together: `x AND y -> z` means to connect wires `x` and `y` to an AND
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gate, and then connect its output to wire `z`.
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For example:
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- `123 -> x` means that the signal `123` is provided to wire `x`.
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- `x AND y -> z` means that the [bitwise
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AND](https://en.wikipedia.org/wiki/Bitwise_operation#AND) of wire
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`x` and wire `y` is provided to wire `z`.
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- `p LSHIFT 2 -> q` means that the value from wire `p` is
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[left-shifted](https://en.wikipedia.org/wiki/Logical_shift) by `2`
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and then provided to wire `q`.
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- `NOT e -> f` means that the [bitwise
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complement](https://en.wikipedia.org/wiki/Bitwise_operation#NOT) of
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the value from wire `e` is provided to wire `f`.
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Other possible gates include `OR` ([bitwise
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OR](https://en.wikipedia.org/wiki/Bitwise_operation#OR)) and `RSHIFT`
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([right-shift](https://en.wikipedia.org/wiki/Logical_shift)). If, for
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some reason, you\'d like to *emulate* the circuit instead, almost all
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programming languages (for example,
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[C](https://en.wikipedia.org/wiki/Bitwise_operations_in_C),
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[JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators),
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or [Python](https://wiki.python.org/moin/BitwiseOperators)) provide
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operators for these gates.
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For example, here is a simple circuit:
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123 -> x
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456 -> y
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x AND y -> d
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x OR y -> e
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x LSHIFT 2 -> f
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y RSHIFT 2 -> g
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NOT x -> h
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NOT y -> i
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After it is run, these are the signals on the wires:
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d: 72
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e: 507
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f: 492
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g: 114
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h: 65412
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i: 65079
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x: 123
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y: 456
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In little Bobby\'s kit\'s instructions booklet (provided as your puzzle
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input), what signal is ultimately provided to *wire `a`*?
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To begin, [get your puzzle input](7/input).
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Answer:
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