feat: add swift implementation to lcof problem: No.56.1 (doocs#2944)

Author: klever34

lcof/面试题56 - I. 数组中数字出现的次数/README.md

@@ -201,6 +201,30 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func singleNumbers(_ nums: [Int]) -> [Int] {
+        var xorSum = 0
+        for num in nums {
+            xorSum ^= num
+        }
+
+        let lowBit = xorSum & -xorSum
+        var a = 0
+        for num in nums {
+            if (num & lowBit) != 0 {
+                a ^= num
+            }
+        }
+
+        let b = xorSum ^ a
+        return [a, b]
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题56 - I. 数组中数字出现的次数/Solution.swift

@@ -0,0 +1,19 @@
+class Solution {
+    func singleNumbers(_ nums: [Int]) -> [Int] {
+        var xorSum = 0
+        for num in nums {
+            xorSum ^= num
+        }
+        
+        let lowBit = xorSum & -xorSum
+        var a = 0
+        for num in nums {
+            if (num & lowBit) != 0 {
+                a ^= num
+            }
+        }
+        
+        let b = xorSum ^ a
+        return [a, b]
+    }
+}