Create 1-Two-Sum.swift

Swift version of Two Sum. Accepted by Leetcode Judge.

swift/1-Two-Sum.swift

@@ -0,0 +1,14 @@
+class Solution {
+ func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
+ var prevMap = [Int:Int]() // val -> index
+
+ for (i, n) in nums.enumerated() {
+ let diff = target - n
+ if let firstIndex = prevMap[diff] {
+ return [firstIndex, i]
+ }
+ prevMap[n] = i
+ }
+ return []
+ }
+}