feat: add swift implementation to lcci problem: No.17.10 (doocs#2782)

Author: klever34

lcci/17.10.Find Majority Element/README.md

@@ -184,6 +184,40 @@ public class Solution {
 }
 ```
 
+```swift
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        var count = 0
+        var candidate: Int?
+
+        for num in nums {
+            if count == 0 {
+                candidate = num
+                count = 1
+            } else if let candidate = candidate, candidate == num {
+                count += 1
+            } else {
+                count -= 1
+            }
+        }
+
+        count = 0
+        if let candidate = candidate {
+            for num in nums {
+                if num == candidate {
+                    count += 1
+                }
+            }
+            if count > nums.count / 2 {
+                return candidate
+            }
+        }
+
+        return -1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.10.Find Majority Element/README_EN.md

@@ -177,6 +177,40 @@ public class Solution {
 }
 ```
 
+```swift
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        var count = 0
+        var candidate: Int?
+
+        for num in nums {
+            if count == 0 {
+                candidate = num
+                count = 1
+            } else if let candidate = candidate, candidate == num {
+                count += 1
+            } else {
+                count -= 1
+            }
+        }
+
+        count = 0
+        if let candidate = candidate {
+            for num in nums {
+                if num == candidate {
+                    count += 1
+                }
+            }
+            if count > nums.count / 2 {
+                return candidate
+            }
+        }
+
+        return -1
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.10.Find Majority Element/Solution.swift

@@ -0,0 +1,31 @@
+class Solution {
+    func majorityElement(_ nums: [Int]) -> Int {
+        var count = 0
+        var candidate: Int?
+
+        for num in nums {
+            if count == 0 {
+                candidate = num
+                count = 1
+            } else if let candidate = candidate, candidate == num {
+                count += 1
+            } else {
+                count -= 1
+            }
+        }
+
+        count = 0
+        if let candidate = candidate {
+            for num in nums {
+                if num == candidate {
+                    count += 1
+                }
+            }
+            if count > nums.count / 2 {
+                return candidate
+            }
+        }
+
+        return -1
+    }
+}