feat: add swift implementation to lcof problem: No.56.2 (doocs#2945)

Author: klever34

lcof/面试题56 - II. 数组中数字出现的次数 II/README.md

@@ -202,6 +202,33 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func singleNumber(_ nums: [Int]) -> Int {
+        var bitCounts = [Int](repeating: 0, count: 32)
+        
+        for num in nums {
+            var x = num
+            for i in 0..<32 {
+                bitCounts[i] += x & 1
+                x >>= 1
+            }
+        }
+        
+        var result = 0
+        for i in 0..<32 {
+            if bitCounts[i] % 3 == 1 {
+                result |= 1 << i
+            }
+        }
+        
+        return result
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

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

@@ -0,0 +1,22 @@
+class Solution {
+    func singleNumber(_ nums: [Int]) -> Int {
+        var bitCounts = [Int](repeating: 0, count: 32)
+        
+        for num in nums {
+            var x = num
+            for i in 0..<32 {
+                bitCounts[i] += x & 1
+                x >>= 1
+            }
+        }
+        
+        var result = 0
+        for i in 0..<32 {
+            if bitCounts[i] % 3 == 1 {
+                result |= 1 << i
+            }
+        }
+        
+        return result
+    }
+}