day 6

3 files changed, 46 insertions, 0 deletions

diff --git a/data/2021/6.txt b/data/2021/6.txt
new file mode 100644
index 0000000..70f9ad7
--- /dev/null
+++ b/data/2021/6.txt
@@ -0,0 +1 @@
+1,4,3,3,1,3,1,1,1,2,1,1,1,4,4,1,5,5,3,1,3,5,2,1,5,2,4,1,4,5,4,1,5,1,5,5,1,1,1,4,1,5,1,1,1,1,1,4,1,2,5,1,4,1,2,1,1,5,1,1,1,1,4,1,5,1,1,2,1,4,5,1,2,1,2,2,1,1,1,1,1,5,5,3,1,1,1,1,1,4,2,4,1,2,1,4,2,3,1,4,5,3,3,2,1,1,5,4,1,1,1,2,1,1,5,4,5,1,3,1,1,1,1,1,1,2,1,3,1,2,1,1,1,1,1,1,1,2,1,1,1,1,2,1,1,1,1,1,1,4,5,1,3,1,4,4,2,3,4,1,1,1,5,1,1,1,4,1,5,4,3,1,5,1,1,1,1,1,5,4,1,1,1,4,3,1,3,3,1,3,2,1,1,3,1,1,4,5,1,1,1,1,1,3,1,4,1,3,1,5,4,5,1,1,5,1,1,4,1,1,1,3,1,1,4,2,3,1,1,1,1,2,4,1,1,1,1,1,2,3,1,5,5,1,4,1,1,1,1,3,3,1,4,1,2,1,3,1,1,1,3,2,2,1,5,1,1,3,2,1,1,5,1,1,1,1,1,1,1,1,1,1,2,5,1,1,1,1,3,1,1,1,1,1,1,1,1,5,5,1
diff --git a/src/2021/6/mod.rs b/src/2021/6/mod.rs
new file mode 100644
index 0000000..ddf7855
--- /dev/null
+++ b/src/2021/6/mod.rs
@@ -0,0 +1,41 @@
+pub fn part1() -> anyhow::Result<i64> {
+    let mut fishes: Vec<u8> = data_lines!()?
+        .next()
+        .unwrap()?
+        .split(',')
+        .map(|s| s.parse())
+        .collect::<Result<_, _>>()?;
+    for _ in 0..80 {
+        let mut new = 0;
+        for fish in fishes.iter_mut() {
+            if *fish == 0 {
+                *fish = 6;
+                new += 1;
+            } else {
+                *fish -= 1;
+            }
+        }
+        fishes.resize(fishes.len() + new, 8);
+    }
+    Ok(fishes.len().try_into()?)
+}
+
+pub fn part2() -> anyhow::Result<i64> {
+    let fishes: Vec<u8> = data_lines!()?
+        .next()
+        .unwrap()?
+        .split(',')
+        .map(|s| s.parse())
+        .collect::<Result<_, _>>()?;
+    let mut by_age = std::collections::VecDeque::new();
+    by_age.resize(9, 0);
+    for fish in fishes {
+        by_age[fish as usize] += 1;
+    }
+    for _ in 0..256 {
+        let new = by_age.pop_front().unwrap();
+        by_age[6] += new;
+        by_age.push_back(new);
+    }
+    Ok(by_age.iter().sum())
+}
diff --git a/src/2021/mod.rs b/src/2021/mod.rs
index a84c726..f4bc3c5 100644
--- a/src/2021/mod.rs
+++ b/src/2021/mod.rs
@@ -8,6 +8,8 @@ mod day3;
 mod day4;
 #[path = "5/mod.rs"]
 mod day5;
+#[path = "6/mod.rs"]
+mod day6;
 // NEXT MOD
 
 pub fn run(day: u8, puzzle: u8) -> anyhow::Result<i64> {
@@ -22,6 +24,8 @@ pub fn run(day: u8, puzzle: u8) -> anyhow::Result<i64> {
         (4, 2) => day4::part2(),
         (5, 1) => day5::part1(),
         (5, 2) => day5::part2(),
+        (6, 1) => day6::part1(),
+        (6, 2) => day6::part2(),
         // NEXT PART
         _ => Err(anyhow::anyhow!("unknown puzzle {}-{}", day, puzzle)),
     }