Added Solution for 2021 day 03

2021/day03_binary_diagnostic/src/lib.rs

@@ -0,0 +1,83 @@
+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)));
+    }
+}