solution: day 20

src/days.rs

@@ -17,7 +17,7 @@ pub mod d16;
 pub mod d17;
 pub mod d18;
 pub mod d19;
-// pub mod d20;
+pub mod d20;
 // pub mod d21;
 // pub mod d22;
 // pub mod d23;

src/days/d20.rs

@@ -0,0 +1,74 @@
+#![allow(unused_imports)]
+use std::ops::RangeInclusive;
+use crate::prelude::*;
+
+pub type I = Vec<RangeInclusive<u64>>;
+pub type O = u64;
+
+fn _parse (data: &str) -> I {
+    data.trim().lines().map(|e| e.trim().split_once('-').map(|(a, b)| a.parse().unwrap()..=b.parse().unwrap()).unwrap()).collect()
+}
+
+fn _silver (mut data: I) -> O {
+    data.sort_by_key(|d| *d.start());
+    let mut start = data[0].end() + 1;
+
+    for d in &data[1..] {
+        if *d.start() <= start {
+            start = start.max(d.end() + 1);
+            continue;
+        }
+
+        return start;
+    }
+
+    Default::default()
+}
+
+fn _gold (mut data: I) -> O {
+    data.sort_by_key(|d| *d.start());
+    let mut start = data[0].end() + 1;
+    let mut gaps = 0;
+
+    for d in &data[1..] {
+        if *d.start() <= start {
+            start = start.max(d.end() + 1);
+            continue;
+        }
+
+        let l = d.start() - start;
+        gaps += l;
+        start = d.end() + 1;
+    }
+
+    // doesn't matter in my input, but for a general case where there's a gap between last
+    // blocked ip and last possible ip will matter. check is here to ensure it won't overflow
+    if start <= u32::MAX as u64 {
+        gaps += u32::MAX as u64 - start;
+    }
+    gaps
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        let data = inc!(20);
+        _parse(data)
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(data);
+        assert_eq!(ans, 17348574)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(data);
+        assert_eq!(ans, 104)
+    }
+}