Create two-sum.cpp

Author: kamyu104

C++/two-sum.cpp

@@ -0,0 +1,18 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        vector<int> res;
+        unordered_map<int, int> lookup;
+        for (int i = 0; i < nums.size(); ++i) {
+            if (lookup.count(target - nums[i])) {
+                res = {lookup[target - nums[i]], i};
+                break;
+            }
+            lookup[nums[i]] = i;
+        }
+        return res;
+    }
+};