feat: add swift implementation to lcof problem: No.42 (doocs#2923)

Author: klever34

lcof/面试题42. 连续子数组的最大和/README.md

@@ -189,6 +189,24 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func maxSubArray(_ nums: [Int]) -> Int {
+        var ans = Int.min
+        var currentSum = 0
+
+        for x in nums {
+            currentSum = max(currentSum, 0) + x
+            ans = max(ans, currentSum)
+        }
+
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题42. 连续子数组的最大和/Solution.swift

@@ -0,0 +1,13 @@
+class Solution {
+    func maxSubArray(_ nums: [Int]) -> Int {
+        var ans = Int.min
+        var currentSum = 0
+        
+        for x in nums {
+            currentSum = max(currentSum, 0) + x
+            ans = max(ans, currentSum)
+        }
+        
+        return ans
+    }
+}