diff --git a/crates/aoc_wasm/web/index.html b/crates/aoc_wasm/web/index.html
index 8d03de8..843a92a 100644
--- a/crates/aoc_wasm/web/index.html
+++ b/crates/aoc_wasm/web/index.html
@@ -15,6 +15,11 @@
             flex-basis: 0;
         }
 
+        #aoc-examples pre:empty::before {
+            content: "\200B"; /* ZWSP */
+            user-select: none;
+        }
+
         .columns > .column {
             min-width: 0;
         }
diff --git a/crates/year2016/src/day20.rs b/crates/year2016/src/day20.rs
new file mode 100644
index 0000000..30e0d85
--- /dev/null
+++ b/crates/year2016/src/day20.rs
@@ -0,0 +1,92 @@
+use utils::prelude::*;
+
+/// Finding numbers outside a list of ranges.
+#[derive(Clone, Debug)]
+pub struct Day20 {
+    ranges: Vec<(u32, u32)>,
+}
+
+impl Day20 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let mut ranges = parser::u32()
+            .then(parser::u32().with_prefix("-"))
+            .map_res(|(min, max)| {
+                if min <= max {
+                    Ok((min, max))
+                } else {
+                    Err("end value cannot be less than start")
+                }
+            })
+            .parse_lines(input)?;
+        ranges.sort_unstable();
+        Ok(Self { ranges })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        let mut ip = 0;
+        for &(start, end) in &self.ranges {
+            if ip < start {
+                break;
+            }
+            if end >= ip {
+                ip = end.checked_add(1).expect("no allowed IPs");
+            }
+        }
+        ip
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> u64 {
+        let mut allowed = 0;
+        let mut ip = 0;
+        for &(start, end) in &self.ranges {
+            if ip < start {
+                allowed += u64::from(start - ip);
+            }
+
+            if end >= ip {
+                let Some(next_ip) = end.checked_add(1) else {
+                    // Range end is u32::MAX, no allowed IPs after final range to add
+                    return allowed;
+                };
+                ip = next_ip;
+            }
+        }
+
+        // Add on IPs after the end of the final range
+        allowed + u64::from(u32::MAX - ip) + 1
+    }
+}
+
+examples!(Day20 -> (u32, u64) [
+    // Custom examples
+    {
+        input: "0-409354575\n\
+            1005171202-1792978424\n\
+            2396795992-4166223847\n\
+            361276686-3509736453\n\
+            2979588951-3460902073",
+        part1: 4166223848,
+        part2: 128743448
+    },
+    {
+        input: "",
+        part1: 0,
+        part2: 4294967296,
+    },
+    {
+        input: "0-0",
+        part1: 1,
+        part2: 4294967295,
+    },
+    {
+        input: "4294967295-4294967295",
+        part1: 0,
+        part2: 4294967295,
+    },
+    {
+        input: "0-4294967295",
+        part2: 0,
+    },
+]);
diff --git a/crates/year2016/src/lib.rs b/crates/year2016/src/lib.rs
index 90898d2..e1d730a 100644
--- a/crates/year2016/src/lib.rs
+++ b/crates/year2016/src/lib.rs
@@ -21,4 +21,5 @@ utils::year!(2016 => year2016, ${
     17 => day17::Day17,
     18 => day18::Day18,
     19 => day19::Day19,
+    20 => day20::Day20,
 });