feat: add swift implementation to lcof problem: No.53.2 (doocs#2939)

Author: klever34

lcof/面试题53 - II. 0～n-1中缺失的数字/README.md

@@ -181,6 +181,27 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func missingNumber(_ nums: [Int]) -> Int {
+        var left = 0
+        var right = nums.count
+
+        while left < right {
+            let mid = (left + right) / 2
+            if nums[mid] > mid {
+                right = mid
+            } else {
+                left = mid + 1
+            }
+        }
+        return left
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题53 - II. 0～n-1中缺失的数字/Solution.swift

@@ -0,0 +1,16 @@
+class Solution {
+    func missingNumber(_ nums: [Int]) -> Int {
+        var left = 0
+        var right = nums.count
+        
+        while left < right {
+            let mid = (left + right) / 2
+            if nums[mid] > mid {
+                right = mid
+            } else {
+                left = mid + 1
+            }
+        }
+        return left
+    }
+}