Added Solution for 2021 day 03

2021/day03_binary_diagnostic/Cargo.toml

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+[package]
+name = "day03_binary_diagnostic"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2021/day03_binary_diagnostic/challenge.txt

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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.
+
+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.)
+
+Your puzzle answer was `2498354`.
+
+\--- 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.)
+
+Your puzzle answer was `3277956`.
+
+Both parts of this puzzle are complete! They provide two gold stars: \*\*
+
+At this point, you should [return to your Advent calendar](/2021) and try another puzzle.
+
+If you still want to see it, you can [get your puzzle input](3/input).

2021/day03_binary_diagnostic/src/lib.rs

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+use core::fmt::Display;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ParseError {
+    ParseIntError(char),
+}
+
+impl Display for ParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::ParseIntError(e) => write!(f, "Unable to parse into integer {e}"),
+        }
+    }
+}
+
+pub fn run(input: &str) -> Result<(usize, usize), ParseError> {
+    let bits: Vec<_> = input.lines().map(|line| line.chars().map(|i| i.to_digit(10).ok_or(ParseError::ParseIntError(i))).collect::<Result<Vec<_>, _>>()).collect::<Result<Vec<_>, _>>()?;
+    let mut ones = vec![0; bits[0].len()];
+    bits.iter().for_each(|number| number.iter().enumerate().for_each(|(idx, bit)| ones[idx] += bit));
+    let half = bits.len() as u32/2;
+    let mut gamma = 0;
+    let mut epsilon = 0;
+    ones.iter().for_each(|bit_count| {
+        gamma *= 2;
+        epsilon *= 2;
+        if bit_count > &half {
+            gamma += 1;
+        } else {
+            epsilon += 1;
+        }
+    });
+    let first = gamma as usize * epsilon as usize;
+
+    let bit_count = bits.len();
+    let mut oxygen_rating = bits.clone();
+    for idx in 0..bit_count {
+        if oxygen_rating.len() > 1 {
+            if oxygen_rating.iter().map(|bits| bits[idx]).sum::<u32>() >= (oxygen_rating.len() as u32 + 1) / 2 {
+                oxygen_rating.retain(|bits| bits[idx] == 1);
+            } else {
+                oxygen_rating.retain(|bits| bits[idx] == 0);
+            }
+        }
+    }
+    let oxygen_rating = oxygen_rating[0].iter().fold(0, |acc, bit| 2 * acc + *bit);
+
+    let mut co2_rating = bits.clone();
+    for idx in 0..bit_count {
+        if co2_rating.len() > 1 {
+            if co2_rating.iter().map(|bits| bits[idx]).sum::<u32>() >= (co2_rating.len() as u32 + 1) / 2 {
+                co2_rating.retain(|bits| bits[idx] == 0);
+            } else {
+                co2_rating.retain(|bits| bits[idx] == 1);
+            }
+        }
+    }
+    let co2_rating = co2_rating[0].iter().fold(0, |acc, bit| 2 * acc + *bit);
+
+    let second = oxygen_rating as usize * co2_rating as usize;
+    Ok((first, second))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs::read_to_string;
+
+    fn read_file(name: &str) -> String {
+        read_to_string(name).expect(&format!("Unable to read file: {name}")[..]).trim().to_string()
+    }
+
+    #[test]
+    fn test_sample() {
+        let sample_input = read_file("tests/sample_input");
+        assert_eq!(run(&sample_input), Ok((198, 230)));
+    }
+
+    #[test]
+    fn test_challenge() {
+        let challenge_input = read_file("tests/challenge_input");
+        assert_eq!(run(&challenge_input), Ok((2498354, 3277956)));
+    }
+}

2021/day03_binary_diagnostic/tests/sample_input

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