feat: add swift solution 2 implementation to lcof2 problem: No.119 (doocs#3713)

Author: klever34

lcof2/剑指 Offer II 119. 最长连续序列/README.md

@@ -388,6 +388,33 @@ var longestConsecutive = function (nums) {
 };
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func longestConsecutive(_ nums: [Int]) -> Int {
+        let numSet: Set<Int> = Set(nums)
+        var longestStreak = 0
+        
+        for num in nums {
+            if !numSet.contains(num - 1) {
+                var currentNum = num
+                var currentStreak = 1
+                
+                while numSet.contains(currentNum + 1) {
+                    currentNum += 1
+                    currentStreak += 1
+                }
+                
+                longestStreak = max(longestStreak, currentStreak)
+            }
+        }
+        
+        return longestStreak
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 119. 最长连续序列/Solution2.swift

@@ -0,0 +1,22 @@
+class Solution {
+    func longestConsecutive(_ nums: [Int]) -> Int {
+        let numSet: Set<Int> = Set(nums)
+        var longestStreak = 0
+        
+        for num in nums {
+            if !numSet.contains(num - 1) {
+                var currentNum = num
+                var currentStreak = 1
+                
+                while numSet.contains(currentNum + 1) {
+                    currentNum += 1
+                    currentStreak += 1
+                }
+                
+                longestStreak = max(longestStreak, currentStreak)
+            }
+        }
+        
+        return longestStreak
+    }
+}