diff --git a/source/contains_duplicate/mod.rs b/source/contains_duplicate/mod.rs
new file mode 100644
index 0000000..97883e4
--- /dev/null
+++ b/source/contains_duplicate/mod.rs
@@ -0,0 +1,8 @@
+pub fn contains_duplicate(numbers: Vec<i32>) -> bool {
+  // Uncomment FromIterator in Leetcode since they're using Rust Edition 2018.
+  // Edition 2021 has this trait in its prelude.
+
+  // use std::iter::FromIterator;
+  std::collections::HashSet::<_>::from_iter(numbers.iter()).len()
+    != numbers.len()
+}
diff --git a/source/lib.rs b/source/lib.rs
index efcc123..9c29e04 100644
--- a/source/lib.rs
+++ b/source/lib.rs
@@ -1,4 +1,5 @@
 pub mod add_binary;
+pub mod contains_duplicate;
 pub mod excel_sheet_column_number;
 pub mod excel_sheet_column_title;
 pub mod implement_strstr;
diff --git a/tests/contains_duplicate.rs b/tests/contains_duplicate.rs
new file mode 100644
index 0000000..b12d687
--- /dev/null
+++ b/tests/contains_duplicate.rs
@@ -0,0 +1,9 @@
+use leetcode::contains_duplicate::contains_duplicate;
+
+use test_case::test_case;
+
+#[test_case(&[1, 2, 3, 1], true; "example 1")]
+#[test_case(&[1, 2, 3, 4], false; "example 2")]
+fn test_contains_duplicate(input: &[i32], expected: bool) {
+  assert_eq!(contains_duplicate(input.to_vec()), expected);
+}