1 files changed, 109 insertions, 0 deletions
diff --git a/src/bin/day3.rs b/src/bin/day3.rs
new file mode 100644
index 0000000..cb442ed
--- /dev/null
+++ b/src/bin/day3.rs
@@ -0,0 +1,109 @@
+fn main() {
+    let input = advent::read_lines(3);
+    println!("3a: {}", power_consumption(&input));
+    println!("3b: {}", life_support_rating(&input));
+}
+
+
+fn power_consumption<T: AsRef<str>>(input: &[T]) -> u32 {
+    let bits = count_ones(input);
+    let gamma = rate(&bits, input.len(), true);
+    let epsilon = rate(&bits, input.len(), false);
+
+    gamma * epsilon
+}
+
+fn count_ones_at_pos<T: AsRef<str>>(input: &[T], pos: usize) -> usize {
+    input.iter()
+         .filter(|&x| x.as_ref().chars().nth(pos).unwrap() == '1')
+         .count()
+}
+
+fn count_ones<T: AsRef<str>>(input: &[T]) -> Vec<usize> {
+    input[0].as_ref()
+            .chars()
+            .enumerate()
+            .map(|(i, _)| count_ones_at_pos(input, i))
+            .collect()
+}
+
+fn rate(bits: &[usize], max_count: usize, gamma: bool) -> u32 {
+    let mut result = 0;
+    let max_count = max_count;
+
+    for count in bits.iter() {
+        result <<= 1;
+        if gamma && 2 * count > max_count {
+            result += 1;
+        }
+        if !gamma && 2 * count < max_count {
+            result += 1;
+        }
+    }
+    result
+}
+
+fn life_support_rating<T: AsRef<str>>(input: &[T]) -> usize {
+    let oxygen = oxygen_rating(input);
+    let co2 = co2_rating(input);
+
+    oxygen * co2
+}
+
+fn co2_rating<T: AsRef<str>>(input: &[T]) -> usize {
+    rating(input, false)
+}
+
+fn oxygen_rating<T: AsRef<str>>(input: &[T]) -> usize {
+    rating(input, true)
+}
+
+fn rating<T: AsRef<str>>(input: &[T], oxygen: bool) -> usize {
+    let mut numbers = vec!["0"; input.len()];
+    for (i, number) in input.iter().enumerate() {
+        numbers[i] = number.as_ref();
+    }
+
+    let len = numbers[0].len();
+    for i in 0 .. len {
+        let ones = count_ones_at_pos(&numbers, i);
+        let keep = if (oxygen && 2 * ones >= numbers.len()) || (!oxygen && 2 * ones < numbers.len()) {
+            '1'
+        } else {
+            '0'
+        };
+        numbers = numbers.iter()
+                         .filter(|&x| x.chars().nth(i).unwrap() == keep)
+                         .copied()
+                         .collect();
+        if numbers.len() == 1 {
+            break;
+        }
+    }
+    usize::from_str_radix(numbers[0], 2).unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "00100",
+            "11110",
+            "10110",
+            "10111",
+            "10101",
+            "01111",
+            "00111",
+            "11100",
+            "10000",
+            "11001",
+            "00010",
+            "01010",
+        ];
+        assert_eq!(power_consumption(&input), 198);
+        assert_eq!(life_support_rating(&input), 230);
+    }
+}