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Year 2021 Day 03 solutions (#9)
- Solve both parts of day 3.
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‎2021/day-03.php

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<?php
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require __DIR__ . '/../vendor/autoload.php';
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use adventofcode\Year2021\Diagnostics;
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/**
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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 produce a diagnostic report just in case.
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*
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* The diagnostic report (your puzzle input) consists of a list of binary numbers which, when decoded properly, can
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* tell you many useful things about the conditions of the submarine. The first parameter to check is the power
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* consumption.
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*
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* You need to use the binary numbers in the diagnostic report to generate two new binary numbers (called the gamma
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* rate and the epsilon rate). The power consumption can then be found by multiplying the gamma rate by the epsilon
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* rate.
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*
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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
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* 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
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* is 1, the first bit of the gamma rate is 1.
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*
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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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*
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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
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* bits of the gamma rate are 110.
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*
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* So, the gamma rate is the binary number 10110, or 22 in decimal.
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*
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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
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* position is used. So, the epsilon rate is 01001, or 9 in decimal. Multiplying the gamma rate (22) by the epsilon
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* rate (9) produces the power consumption, 198.
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*
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* Use the binary numbers in your diagnostic report to calculate the gamma rate and epsilon rate, then multiply them
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* together. What is the power consumption of the submarine? (Be sure to represent your answer in decimal, not binary.)
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*/
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$diagnostics = new Diagnostics();
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$readings = file(__DIR__ . '/inputs/day-03.input', FILE_IGNORE_NEW_LINES);
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$powerConsumption = $diagnostics->findPowerConsumption($readings);
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$product = $powerConsumption['epsilon'] * $powerConsumption['gamma'];
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print(
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'Your epsilon value is ' . $powerConsumption['epsilon'] . ' and your gamma value is '
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. $powerConsumption['gamma'] . ' for a product of ' . $product . ".\n"
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);
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/**
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* --- Part Two ---
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* Next, you should verify the life support rating, which can be determined by multiplying the oxygen generator rating
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* by the CO2 scrubber rating.
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*
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* Both the oxygen generator rating and the CO2 scrubber rating are values that can be found in your diagnostic
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* report - finding them is the tricky part. Both values are located using a similar process that involves filtering
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* out values until only one remains. Before searching for either rating value, start with the full list of binary
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* numbers from your diagnostic report and consider just the first bit of those numbers. Then:
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*
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* - Keep only numbers selected by the bit criteria for the type of rating value for which you are searching. Discard
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* 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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*
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* The bit criteria depends on which type of rating value you want to find:
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*
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* - To find oxygen generator rating, determine the most common value (0 or 1) in the current bit position, and keep
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* only numbers with that bit in that position. If 0 and 1 are equally common, keep values with a 1 in the position
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* 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
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* numbers with that bit in that position. If 0 and 1 are equally common, keep values with a 0 in the position being
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* considered.
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*
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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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*
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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
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* bits (5), so keep only the 7 numbers with a 1 in the first position: 11110, 10110, 10111, 10101, 11100, 10000,
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* 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
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* 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
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* 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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*
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* Then, to determine the CO2 scrubber rating value from the same example above:
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*
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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
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* 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
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* 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
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* 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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*
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* Finally, to find the life support rating, multiply the oxygen generator rating (23) by the CO2 scrubber
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* rating (10) to get 230.
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*
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* Use the binary numbers in your diagnostic report to calculate the oxygen generator rating and CO2 scrubber rating,
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* then multiply them together. What is the life support rating of the submarine? (Be sure to represent your answer
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* in decimal, not binary.)
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*/
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$lifeSupportRating = $diagnostics->findLifeSupportRating($readings);
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$product = $lifeSupportRating['oxygen generator'] * $lifeSupportRating['co2 scrubber'];
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print(
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'Your oxygen generator rating is ' . $lifeSupportRating['oxygen generator'] . ' and your CO2 scrubber rating is '
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. $lifeSupportRating['co2 scrubber'] . ' for a product of ' . $product . ".\n"
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);

‎2021/inputs/day-03-sample.input

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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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