feat: add swift implementation to lcci problem: No.08.03 (#2685)

Author: klever34

lcci/08.03.Magic Index/README.md

@@ -222,6 +222,31 @@ impl Solution {
 }
 ```
 
+```swift
+class Solution {
+    func findMagicIndex(_ nums: [Int]) -> Int {
+        let left = 0
+        let right = nums.count - 1
+        return find(nums, left, right)
+    }
+
+    private func find(_ nums: [Int], _ left: Int, _ right: Int) -> Int {
+        if left > right {
+            return -1
+        }
+        let mid = (left + right) >> 1
+        let leftIndex = find(nums, left, mid - 1)
+        if leftIndex != -1 {
+            return leftIndex
+        }
+        if nums[mid] == mid {
+            return mid
+        }
+        return find(nums, mid + 1, right)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/08.03.Magic Index/README_EN.md

@@ -228,6 +228,31 @@ impl Solution {
 }
 ```
 
+```swift
+class Solution {
+    func findMagicIndex(_ nums: [Int]) -> Int {
+        let left = 0
+        let right = nums.count - 1
+        return find(nums, left, right)
+    }
+
+    private func find(_ nums: [Int], _ left: Int, _ right: Int) -> Int {
+        if left > right {
+            return -1
+        }
+        let mid = (left + right) >> 1
+        let leftIndex = find(nums, left, mid - 1)
+        if leftIndex != -1 {
+            return leftIndex
+        }
+        if nums[mid] == mid {
+            return mid
+        }
+        return find(nums, mid + 1, right)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/08.03.Magic Index/Solution.swift

@@ -0,0 +1,22 @@
+class Solution {
+    func findMagicIndex(_ nums: [Int]) -> Int {
+        let left = 0
+        let right = nums.count - 1
+        return find(nums, left, right)
+    }
+
+    private func find(_ nums: [Int], _ left: Int, _ right: Int) -> Int {
+        if left > right {
+            return -1
+        }
+        let mid = (left + right) >> 1
+        let leftIndex = find(nums, left, mid - 1)
+        if leftIndex != -1 {
+            return leftIndex
+        }
+        if nums[mid] == mid {
+            return mid
+        }
+        return find(nums, mid + 1, right)
+    }
+}