1 files changed, 42 insertions, 0 deletions
diff --git a/src/bin/2021/day7.rs b/src/bin/2021/day7.rs
new file mode 100644
index 0000000..56eaeb1
--- /dev/null
+++ b/src/bin/2021/day7.rs
@@ -0,0 +1,42 @@
+use advent_of_code::prelude::*;
+
+pub fn parse(fh: File) -> Result<Vec<usize>> {
+    Ok(parse::split(fh, b',').collect())
+}
+
+pub fn part1(crabs: Vec<usize>) -> Result<usize> {
+    Ok((0..=crabs.iter().copied().max().unwrap())
+        .map(|start| {
+            crabs.iter().copied().map(|crab| crab.abs_diff(start)).sum()
+        })
+        .min()
+        .unwrap())
+}
+
+pub fn part2(crabs: Vec<usize>) -> Result<usize> {
+    Ok((0..=crabs.iter().copied().max().unwrap())
+        .map(|start| {
+            crabs
+                .iter()
+                .copied()
+                .map(|crab| {
+                    let diff = crab.abs_diff(start);
+                    diff * (diff + 1) / 2
+                })
+                .sum()
+        })
+        .min()
+        .unwrap())
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2021, 7).unwrap()).unwrap()).unwrap(),
+        333755
+    );
+    assert_eq!(
+        part2(parse(parse::data(2021, 7).unwrap()).unwrap()).unwrap(),
+        94017638
+    );
+}