diff --git a/Cargo.lock b/Cargo.lock
index e7a218e..a252cd3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6,6 +6,10 @@ version = 3
 name = "contains-duplicate"
 version = "0.1.0"
 
+[[package]]
+name = "two_sum"
+version = "0.1.0"
+
 [[package]]
 name = "valid_anagram"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index 6aa60b8..f749b8a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,5 +3,9 @@ pedantic = "warn"
 nursery = "warn"
 
 [workspace]
-members = ["crates/contains_duplicate", "crates/valid_anagram"]
+members = [
+	"crates/contains_duplicate",
+	"crates/two_sum",
+	"crates/valid_anagram",
+]
 resolver = "2"
diff --git a/crates/two_sum/Cargo.toml b/crates/two_sum/Cargo.toml
new file mode 100644
index 0000000..0b0bd5c
--- /dev/null
+++ b/crates/two_sum/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "two_sum"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+
+[lints]
+workspace = true
diff --git a/crates/two_sum/src/lib.rs b/crates/two_sum/src/lib.rs
new file mode 100644
index 0000000..65059cf
--- /dev/null
+++ b/crates/two_sum/src/lib.rs
@@ -0,0 +1,42 @@
+use std::collections::HashMap;
+
+#[must_use]
+pub fn two_sum(nums: Vec<i32>, target: i32) -> Vec<i32> {
+	let mut map = HashMap::new();
+
+	for (i, number) in nums.into_iter().enumerate() {
+		let diff = target - number;
+
+		if let Some(&j) = map.get(&diff) {
+			#[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
+			return vec![i as i32, j as i32];
+		}
+
+		map.insert(number, i);
+	}
+
+	unreachable!()
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn case_1() {
+		let result = two_sum(vec![2, 7, 11, 15], 9);
+		assert_eq!(result, [0, 1]);
+	}
+
+	#[test]
+	fn case_2() {
+		let result = two_sum(vec![3, 2, 4], 6);
+		assert_eq!(result, [1, 2]);
+	}
+
+	#[test]
+	fn case_3() {
+		let result = two_sum(vec![3, 3], 6);
+		assert_eq!(result, [0, 1]);
+	}
+}