diff --git a/2019/04/Cargo.toml b/2019/04/Cargo.toml
new file mode 100644
index 0000000..7df0553
--- /dev/null
+++ b/2019/04/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "d4"
+version = "0.1.0"
+authors = ["kageru <kageru@encode.moe>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+itertools = "0.8.2"
diff --git a/2019/04/src/main.rs b/2019/04/src/main.rs
new file mode 100644
index 0000000..1101a46
--- /dev/null
+++ b/2019/04/src/main.rs
@@ -0,0 +1,25 @@
+#![feature(is_sorted)]
+use itertools::Itertools;
+
+pub fn main() {
+    let (lower, upper) = (172930, 683082);
+    let valid_part1 = (lower..upper)
+        .map(|n| n.to_string().chars().collect::<Vec<_>>())
+        .filter(|n| n.is_sorted())
+        .filter(|v| v.clone().iter().dedup().count() != v.len());
+    println!("Part 1: {}", valid_part1.clone().count());
+    let part2 = valid_part1
+        .filter(|v| {
+            let (mut last, mut streak, mut double) = (' ', 0, false);
+            v.iter().for_each(|c| {
+                if streak == 2 && c != &last {
+                    double = true
+                }
+                streak = if c == &last { streak + 1 } else { 1 };
+                last = *c;
+            });
+            double || streak == 2
+        })
+        .count();
+    println!("Part 2: {}", part2);
+}