day 3 and 4 solutions

src/day03.rs

@@ -0,0 +1,114 @@
+use crate::utils::read_file;
+use anyhow::Result;
+
+fn strings_to_ints(s: &str) -> Vec<usize> {
+    s.lines()
+        .map(|line| usize::from_str_radix(line, 2).unwrap())
+        .collect()
+}
+
+fn diagnose_power(s: &str) -> usize {
+    // collect all positions with ones
+    let bits = s.lines().next().unwrap().len();
+    let n_words = s.lines().count();
+    let mut counts = vec![0; bits];
+    s.lines().for_each(|line| {
+        line.chars().enumerate().for_each(|(i, c)| {
+            if c == '1' {
+                counts[i] += 1;
+            }
+        })
+    });
+
+    // determine whether zero or one is greatter than half for each position
+    let ret: String = counts
+        .iter()
+        .map(|n| if n > &(n_words / 2) { '1' } else { '0' })
+        .collect();
+
+    // put together gamma (all majority 1 slots) and epsilon (!gamma)
+    let gamma = usize::from_str_radix(&ret, 2).unwrap();
+    let epsilon = !gamma & ((1 << bits) - 1);
+    gamma * epsilon
+}
+
+fn find_oxygen_or_co2(s: &str, oxygen: bool) -> usize {
+    let bits = s.lines().next().unwrap().len();
+    let mut kept = strings_to_ints(s);
+    usize::from_str_radix(
+        &(0..bits)
+            .rev()
+            .map(|bit| {
+                // split current set into ones/zeroes for current bit
+                let mut ones = vec![];
+                let mut zeroes = vec![];
+                kept.iter().for_each(|x| {
+                    if x & (1 << bit) != 0 {
+                        ones.push(*x);
+                    } else {
+                        zeroes.push(*x);
+                    }
+                });
+
+                if kept.len() == 1 {
+                    // only one left so we take its 0 or 1 regardless
+                    if kept[0] & (1 << bit) != 0 {
+                        '1'
+                    } else {
+                        '0'
+                    }
+                } else if oxygen {
+                    // keep whichever has the most, ties are 1
+                    if ones.len() >= zeroes.len() {
+                        kept = ones;
+                        '1'
+                    } else {
+                        kept = zeroes;
+                        '0'
+                    }
+                } else {
+                    // keep whichever has the least, ties are 0
+                    if zeroes.len() <= ones.len() {
+                        kept = zeroes;
+                        '0'
+                    } else {
+                        kept = ones;
+                        '1'
+                    }
+                }
+            })
+            .collect::<String>(),
+        2,
+    )
+    .unwrap()
+}
+fn diagnose_lifesupport(s: &str) -> usize {
+    let oxygen_generator = find_oxygen_or_co2(s, true);
+    let co2_scrubber = find_oxygen_or_co2(s, false);
+    oxygen_generator * co2_scrubber
+}
+
+pub(crate) fn run() -> Result<(usize, usize)> {
+    let input = read_file("data/day03.txt")?;
+    Ok((diagnose_power(&input), diagnose_lifesupport(&input)))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        let input = read_file("data/day03-test.txt").unwrap();
+        assert_eq!(diagnose_power(&input), 198);
+        assert_eq!(diagnose_lifesupport(&input), 230);
+    }
+
+    #[test]
+    fn test_my_data() {
+        let input = read_file("data/day03.txt").unwrap();
+        assert_eq!(diagnose_power(&input), 4191876);
+        // assert_eq!(follow_course(&input), 2070300);
+        // assert_eq!(follow_course_better(&input), 2078985210);
+    }
+}