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60 lines
2.0 KiB
Markdown
60 lines
2.0 KiB
Markdown
3 years ago
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https://adventofcode.com/2021/day/3
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## \--- Day 3: Binary Diagnostic ---
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The submarine has been making some odd creaking noises, so you ask it to
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produce a diagnostic report just in case.
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The diagnostic report (your puzzle input) consists of a list of binary numbers
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which, when decoded properly, can tell you many useful things about the
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conditions of the submarine. The first parameter to check is the _power
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consumption_.
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You need to use the binary numbers in the diagnostic report to generate two
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new binary numbers (called the _gamma rate_ and the _epsilon rate_ ). The
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power consumption can then be found by multiplying the gamma rate by the
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epsilon rate.
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Each bit in the gamma rate can be determined by finding the _most common bit
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in the corresponding position_ of all numbers in the diagnostic report. For
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example, given the following diagnostic report:
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[code]
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00100
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11110
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10110
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10111
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10101
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01111
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00111
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11100
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10000
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11001
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00010
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01010
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[/code]
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Considering only the first bit of each number, there are five `0` bits and
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seven `1` bits. Since the most common bit is `1`, the first bit of the gamma
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rate is `1`.
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The most common second bit of the numbers in the diagnostic report is `0`, so
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the second bit of the gamma rate is `0`.
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The most common value of the third, fourth, and fifth bits are `1`, `1`, and
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`0`, respectively, and so the final three bits of the gamma rate are `110`.
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So, the gamma rate is the binary number `10110`, or `_22_` in decimal.
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The epsilon rate is calculated in a similar way; rather than use the most
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common bit, the least common bit from each position is used. So, the epsilon
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rate is `01001`, or `_9_` in decimal. Multiplying the gamma rate (`22`) by the
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epsilon rate (`9`) produces the power consumption, `_198_`.
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Use the binary numbers in your diagnostic report to calculate the gamma rate
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and epsilon rate, then multiply them together. _What is the power consumption
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of the submarine?_ (Be sure to represent your answer in decimal, not binary.)
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