feat(exercises): add LeetCode-style 'Two Sum' problem in new leetcode module

exercises/leetcode/two_sum.rs

@@ -0,0 +1,23 @@
+// TODO: Implement the "Two Sum" problem in Rust.
+// Given an array of integers `nums` and an integer `target`,
+// return the indices of the two numbers such that they add up to `target`.
+//
+// Hint: Try using a HashMap for O(n) time.
+// Remember ownership & borrowing rules for inserting into the map.
+
+pub fn two_sum(nums: Vec<i32>, target: i32) -> Vec<i32> {
+    // Your code here
+    todo!()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_two_sum() {
+        assert_eq!(two_sum(vec![2, 7, 11, 15], 9), vec![0, 1]);
+        assert_eq!(two_sum(vec![3, 2, 4], 6), vec![1, 2]);
+        assert_eq!(two_sum(vec![3, 3], 6), vec![0, 1]);
+    }
+}

rustlings-macros/info.toml

@@ -1209,3 +1209,8 @@ name = "as_ref_mut"
 dir = "23_conversions"
 hint = """
 Add `AsRef<str>` or `AsMut<u32>` as a trait bound to the functions."""
+
+[[exercises]]
+name = "two_sum"
+dir = "leetcode"
+hint = "Use a HashMap to check if the complement exists."