81 lines
No EOL
5.9 KiB
Text
81 lines
No EOL
5.9 KiB
Text
The submarine has been making some odd creaking noises, so you ask it to produce a diagnostic report just in case.
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The diagnostic report (your puzzle input) consists of a list of binary numbers which, when decoded properly, can tell you many useful things about the conditions of the submarine. The first parameter to check is the *power consumption*.
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You need to use the binary numbers in the diagnostic report to generate two new binary numbers (called the *gamma rate* and the *epsilon rate*). The power consumption can then be found by multiplying the gamma rate by the epsilon rate.
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Each bit in the gamma rate can be determined by finding the *most common bit in the corresponding position* of all numbers in the diagnostic report. For example, given the following diagnostic report:
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```
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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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```
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Considering only the first bit of each number, there are five `0` bits and seven `1` bits. Since the most common bit is `1`, the first bit of the gamma rate is `1`.
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The most common second bit of the numbers in the diagnostic report is `0`, so 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 `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 common bit, the least common bit from each position is used. So, the epsilon rate is `01001`, or `*9*` in decimal. Multiplying the gamma rate (`22`) by the 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 and epsilon rate, then multiply them together. *What is the power consumption of the submarine?* (Be sure to represent your answer in decimal, not binary.)
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Your puzzle answer was `2498354`.
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\--- Part Two ---
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----------
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Next, you should verify the *life support rating*, which can be determined by multiplying the *oxygen generator rating* by the *CO2 scrubber rating*.
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Both the oxygen generator rating and the CO2 scrubber rating are values that can be found in your diagnostic report - finding them is the tricky part. Both values are located using a similar process that involves filtering out values until only one remains. Before searching for either rating value, start with the full list of binary numbers from your diagnostic report and *consider just the first bit* of those numbers. Then:
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* Keep only numbers selected by the *bit criteria* for the type of rating value for which you are searching. Discard numbers which do not match the bit criteria.
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* If you only have one number left, stop; this is the rating value for which you are searching.
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* Otherwise, repeat the process, considering the next bit to the right.
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The *bit criteria* depends on which type of rating value you want to find:
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* To find *oxygen generator rating*, determine the *most common* value (`0` or `1`) in the current bit position, and keep only numbers with that bit in that position. If `0` and `1` are equally common, keep values with a `*1*` in the position being considered.
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* To find *CO2 scrubber rating*, determine the *least common* value (`0` or `1`) in the current bit position, and keep only numbers with that bit in that position. If `0` and `1` are equally common, keep values with a `*0*` in the position being considered.
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For example, to determine the *oxygen generator rating* value using the same example diagnostic report from above:
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* Start with all 12 numbers and consider only the first bit of each number. There are more `1` bits (7) than `0` bits (5), so keep only the 7 numbers with a `1` in the first position: `11110`, `10110`, `10111`, `10101`, `11100`, `10000`, and `11001`.
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* Then, consider the second bit of the 7 remaining numbers: there are more `0` bits (4) than `1` bits (3), so keep only the 4 numbers with a `0` in the second position: `10110`, `10111`, `10101`, and `10000`.
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* In the third position, three of the four numbers have a `1`, so keep those three: `10110`, `10111`, and `10101`.
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* In the fourth position, two of the three numbers have a `1`, so keep those two: `10110` and `10111`.
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* In the fifth position, there are an equal number of `0` bits and `1` bits (one each). So, to find the *oxygen generator rating*, keep the number with a `1` in that position: `10111`.
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* As there is only one number left, stop; the *oxygen generator rating* is `10111`, or `*23*` in decimal.
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Then, to determine the *CO2 scrubber rating* value from the same example above:
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* Start again with all 12 numbers and consider only the first bit of each number. There are fewer `0` bits (5) than `1` bits (7), so keep only the 5 numbers with a `0` in the first position: `00100`, `01111`, `00111`, `00010`, and `01010`.
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* Then, consider the second bit of the 5 remaining numbers: there are fewer `1` bits (2) than `0` bits (3), so keep only the 2 numbers with a `1` in the second position: `01111` and `01010`.
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* In the third position, there are an equal number of `0` bits and `1` bits (one each). So, to find the *CO2 scrubber rating*, keep the number with a `0` in that position: `01010`.
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* As there is only one number left, stop; the *CO2 scrubber rating* is `01010`, or `*10*` in decimal.
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Finally, to find the life support rating, multiply the oxygen generator rating (`23`) by the CO2 scrubber rating (`10`) to get `*230*`.
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Use the binary numbers in your diagnostic report to calculate the oxygen generator rating and CO2 scrubber rating, then multiply them together. *What is the life support rating of the submarine?* (Be sure to represent your answer in decimal, not binary.)
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Your puzzle answer was `3277956`.
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Both parts of this puzzle are complete! They provide two gold stars: \*\*
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At this point, you should [return to your Advent calendar](/2021) and try another puzzle.
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If you still want to see it, you can [get your puzzle input](3/input). |