Day 3

Cargo.toml

@@ -10,3 +10,7 @@ path = "src/day1.rs"
 [[bin]]
 name = "day2"
 path = "src/day2.rs"
+
+[[bin]]
+name = "day3"
+path = "src/day3.rs"

src/day3.rs

@@ -0,0 +1,111 @@
+use std::io::{self, BufRead};
+
+fn most_common_bits(report: &Vec<String>) -> String {
+    (0..12)
+        .map(|i| {
+            let counts = report
+                .iter()
+                .fold((0, 0), |acc, x| match x.chars().nth(i).unwrap() {
+                    '0' => (acc.0 + 1, acc.1),
+                    '1' => (acc.0, acc.1 + 1),
+                    _ => acc,
+                });
+            if counts.0 > counts.1 {
+                '0'
+            } else {
+                '1'
+            }
+        })
+        .collect()
+}
+
+fn most_common_value(report: Vec<String>, n: usize) -> Option<String> {
+    (0..n)
+        .fold(report, |r, i| {
+            if r.len() > 1 {
+                let counts = r
+                    .iter()
+                    .fold((0, 0), |acc, x| match x.chars().nth(i).unwrap() {
+                        '0' => (acc.0 + 1, acc.1),
+                        '1' => (acc.0, acc.1 + 1),
+                        _ => acc,
+                    });
+                r.iter()
+                    .filter(|x| match x.chars().nth(i).unwrap() {
+                        '0' if counts.0 > counts.1 => true,
+                        '1' if counts.0 <= counts.1 => true,
+                        _ => false,
+                    })
+                    .cloned()
+                    .collect()
+            } else {
+                r
+            }
+        })
+        .first()
+        .cloned()
+}
+
+fn least_common_value(report: Vec<String>) -> Option<String> {
+    (0..12)
+        .fold(report, |r, i| {
+            if r.len() > 1 {
+                let counts = r
+                    .iter()
+                    .fold((0, 0), |acc, x| match x.chars().nth(i).unwrap() {
+                        '0' => (acc.0 + 1, acc.1),
+                        '1' => (acc.0, acc.1 + 1),
+                        _ => acc,
+                    });
+                r.iter()
+                    .filter(|x| match x.chars().nth(i).unwrap() {
+                        '0' if counts.0 <= counts.1 => true,
+                        '1' if counts.0 > counts.1 => true,
+                        _ => false,
+                    })
+                    .cloned()
+                    .collect()
+            } else {
+                r
+            }
+        })
+        .first()
+        .cloned()
+}
+
+fn main() {
+    const INPUT: &'static str = include_str!("../inputs/day3.txt");
+    let report: Vec<String> = io::Cursor::new(INPUT).lines().map(|l| l.unwrap()).collect();
+    let gamma_rate = u32::from_str_radix(&most_common_bits(&report), 2).unwrap();
+    let epsilon_rate = 0xfff ^ gamma_rate;
+    println!("gamma rate {} epsilon rate {}", gamma_rate, epsilon_rate);
+    println!("solution {}", gamma_rate * epsilon_rate);
+
+    let oxygen_generator_rating =
+        u32::from_str_radix(&most_common_value(report.clone(), 12).unwrap(), 2).unwrap();
+    println!("oxygen generator rating {}", oxygen_generator_rating);
+
+    let co2_scrubber_rating = u32::from_str_radix(&least_common_value(report).unwrap(), 2).unwrap();
+    println!("CO2 scrubber rating {}", co2_scrubber_rating);
+
+    println!("solution {}", oxygen_generator_rating * co2_scrubber_rating);
+}
+
+#[test]
+fn oxygen_generator_rating() {
+    let report = vec![
+        "00100".to_string(),
+        "11110".to_string(),
+        "10110".to_string(),
+        "10111".to_string(),
+        "10101".to_string(),
+        "01111".to_string(),
+        "00111".to_string(),
+        "11100".to_string(),
+        "10000".to_string(),
+        "11001".to_string(),
+        "00010".to_string(),
+        "01010".to_string(),
+    ];
+    assert_eq!(most_common_value(report, 5).unwrap(), "10111");
+}