feat: add swift implementation to lcof problem: No.39 (#2920)

lcof/面试题39. 数组中出现次数超过一半的数字/README.md

@@ -196,6 +196,27 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        var cnt = 0
+        var m = 0
+
+        for v in nums {
+            if cnt == 0 {
+                m = v
+                cnt = 1
+            } else {
+                cnt += (m == v ? 1 : -1)
+            }
+        }
+        return m
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题39. 数组中出现次数超过一半的数字/Solution.swift

@@ -0,0 +1,16 @@
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        var cnt = 0
+        var m = 0
+        
+        for v in nums {
+            if cnt == 0 {
+                m = v
+                cnt = 1
+            } else {
+                cnt += (m == v ? 1 : -1)
+            }
+        }
+        return m
+    }
+}