diff --git a/sum.py b/sum.py
new file mode 100644
index 0000000000..acd68e1d58
--- /dev/null
+++ b/sum.py
@@ -0,0 +1,16 @@
+from typing import List
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        seen = {}  # value -> index
+        for i, num in enumerate(nums):
+            diff = target - num
+            if diff in seen:
+                return [seen[diff], i]
+            seen[num] = i
+
+# Example usage (not needed on LeetCode; shown for local testing)
+if __name__ == "__main__":
+    print(Solution().twoSum([2,7,11,15], 9))   # [0, 1]
+    print(Solution().twoSum([3,2,4], 6))       # [1, 2]
+    print(Solution().twoSum([3,3], 6))         # [0, 1]