jameshulse · December 5, 2021 04:13 · Dec 5, 2021 · Dec 5, 2021
diff --git a/main.rs → day3.rs b/main.rs → day3.rs
diff --git a/main.rs b/main.rs
@@ -0,0 +1,106 @@
+use indoc::indoc;
+use itertools::Itertools;
+
+fn main() {
+    let lines = include_str!("input");
+
+    dbg!(part_one(lines));
+    dbg!(part_two(lines));
+}
+
+fn part_one(input: &str) -> usize {
+    let lines: Vec<&str> = input.lines().collect_vec();
+    let report_count = lines.len();
+    let report_width = lines[0].len();
+
+    let mut gamma = 0;
+    let mut epsilon = 0;
+
+    for i in 0..report_width {
+        if lines
+            .iter()
+            .map(|l| (l[i..i + 1]).parse::<usize>().unwrap())
+            .sum::<usize>()
+            < report_count / 2
+        {
+            // More zeros
+            epsilon |= 1 << (report_width - i - 1);
+        } else {
+            // More ones
+            gamma |= 1 << (report_width - i - 1);
+        }
+    }
+
+    gamma * epsilon
+}
+
+enum Commonality {
+    Most,
+    Least,
+}
+
+fn part_two(input: &str) -> usize {
+    let oxygen = find_report(input, Commonality::Most);
+    let scrubber = find_report(input, Commonality::Least);
+
+    oxygen * scrubber
+}
+
+fn find_report(input: &str, commonality: Commonality) -> usize {
+    let mut lines: Vec<&str> = input.lines().collect_vec();
+
+    for i in 0..lines[0].len() {
+        let ones = lines
+            .iter()
+            .map(|l| (l[i..i + 1]).parse::<usize>().unwrap())
+            .sum::<usize>();
+        let zeros = lines.len() - ones;
+        let find_digit = match commonality {
+            Commonality::Most => {
+                if ones >= zeros {
+                    "1"
+                } else {
+                    "0"
+                }
+            }
+            Commonality::Least => {
+                if ones >= zeros {
+                    "0"
+                } else {
+                    "1"
+                }
+            }
+        };
+
+        lines.retain(|&l| &l[i..i + 1] == find_digit);
+
+        if lines.len() == 1 {
+            println!("One line remaining: {:?}", lines[0]);
+
+            return usize::from_str_radix(lines[0], 2).unwrap();
+        }
+    }
+
+    0
+}
+
+#[test]
+fn test_parts() {
+    let input = indoc! {"
+        00100
+        11110
+        10110
+        10111
+        10101
+        01111
+        00111
+        11100
+        10000
+        11001
+        00010
+        01010"
+    };
+
+    assert_eq!(part_one(input), 198);
+    assert_eq!(part_two(input), 230);
+}