Year 2021 Day 03 solutions

2021/day-03.php

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+<?php
+
+require __DIR__ . '/../vendor/autoload.php';
+
+use adventofcode\Year2021\Diagnostics;
+
+/**
+ * --- Day 3: Binary Diagnostic ---
+ * The submarine has been making some odd creaking noises, so you ask it to produce a diagnostic report just in case.
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * 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:
+ *
+ * 00100
+ * 11110
+ * 10110
+ * 10111
+ * 10101
+ * 01111
+ * 00111
+ * 11100
+ * 10000
+ * 11001
+ * 00010
+ * 01010
+ *
+ * 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.
+ *
+ * The most common second bit of the numbers in the diagnostic report is 0, so the second bit of the gamma rate is 0.
+ *
+ * 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.
+ *
+ * So, the gamma rate is the binary number 10110, or 22 in decimal.
+ *
+ * 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.
+ *
+ * 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.)
+ */
+
+$diagnostics = new Diagnostics();
+
+$readings = file(__DIR__ . '/inputs/day-03.input', FILE_IGNORE_NEW_LINES);
+$powerConsumption = $diagnostics->findPowerConsumption($readings);
+$product = $powerConsumption['epsilon'] * $powerConsumption['gamma'];
+print(
+    'Your epsilon value is ' . $powerConsumption['epsilon'] . ' and your gamma value is '
+    . $powerConsumption['gamma'] . ' for a product of ' . $product . ".\n"
+);
+
+/**
+ * --- Part Two ---
+ * Next, you should verify the life support rating, which can be determined by multiplying the oxygen generator rating
+ * by the CO2 scrubber rating.
+ *
+ * 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:
+ *
+ * - 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.
+ * - If you only have one number left, stop; this is the rating value for which you are searching.
+ * - Otherwise, repeat the process, considering the next bit to the right.
+ *
+ * The bit criteria depends on which type of rating value you want to find:
+ *
+ * - 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.
+ * - 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.
+ *
+ * For example, to determine the oxygen generator rating value using the same example diagnostic report from above:
+ *
+ * - 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.
+ * - 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.
+ * - In the third position, three of the four numbers have a 1, so keep those three: 10110, 10111, and 10101.
+ * - In the fourth position, two of the three numbers have a 1, so keep those two: 10110 and 10111.
+ * - 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.
+ * - As there is only one number left, stop; the oxygen generator rating is 10111, or 23 in decimal.
+ *
+ * Then, to determine the CO2 scrubber rating value from the same example above:
+ *
+ * - 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.
+ * - 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.
+ * - 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.
+ * - As there is only one number left, stop; the CO2 scrubber rating is 01010, or 10 in decimal.
+ *
+ * Finally, to find the life support rating, multiply the oxygen generator rating (23) by the CO2 scrubber
+ * rating (10) to get 230.
+ *
+ * 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.)
+ */
+
+$lifeSupportRating = $diagnostics->findLifeSupportRating($readings);
+$product = $lifeSupportRating['oxygen generator'] * $lifeSupportRating['co2 scrubber'];
+print(
+    'Your oxygen generator rating is ' . $lifeSupportRating['oxygen generator'] . ' and your CO2 scrubber rating is '
+    . $lifeSupportRating['co2 scrubber'] . ' for a product of ' . $product . ".\n"
+);

2021/inputs/day-03-sample.input

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+00100
+11110
+10110
+10111
+10101
+01111
+00111
+11100
+10000
+11001
+00010
+01010