Update solution to Two Sum

Author: Yi Gu

Array/TwoSum.swift

@@ -2,24 +2,21 @@
  * Question Link: https://leetcode.com/problems/two-sum/
  * Primary idea: Traverse the array and store target - nums[i] in a dict
  *
- * Time Complexity: O(n), Space Complexity: O(nC2)
+ * Time Complexity: O(n), Space Complexity: O(n)
  */
 
 class TwoSum {
-    func twoSum(nums: [Int], _ target: Int) -> [Int] {
-        var res = [Int]()
+    func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
         var dict = [Int: Int]()
-        
+  
         for (i, num) in nums.enumerated() {
-            guard let lastIndex = dict[target - num] else {
-                dict[num] = i
-                continue
+            if let lastIndex = dict[target - num] {
+                return [lastIndex, i]
             }
-            
-            res.append(lastIndex)
-            res.append(i)
+    
+            dict[num] = i
         }
-        
-        return res
+  
+        fatalError("No valid outputs")
     }
 }

README.md

@@ -46,7 +46,7 @@
 [Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)| [Swift](./Array/RemoveDuplicatesFromSortedArrayII.swift)| Medium| O(n)| O(1)|
 [Move Zeroes](https://leetcode.com/problems/move-zeroes/)| [Swift](./Array/MoveZeroes.swift)| Easy| O(n)| O(1)|
 [Remove Element](https://leetcode.com/problems/remove-element/)| [Swift](./Array/RemoveElement.swift)| Easy| O(n)| O(1)|
-[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| O(n)| O(nC2)|
+[Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| O(n)| O(n)|
 [3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
 [3Sum Closest](https://leetcode.com/problems/3sum-closest/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
 [4Sum](https://leetcode.com/problems/4sum/)| [Swift](./Array/FourSum.swift)| Medium| O(n^3)| O(nC4)|