feat: add swift implementation to lcof problem: No.26 (doocs#2893)

Author: klever34

lcof/面试题26. 树的子结构/README.md

@@ -345,6 +345,44 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+/* public class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+* }
+*/
+
+class Solution {
+    func isSubStructure(_ A: TreeNode?, _ B: TreeNode?) -> Bool {
+        guard let A = A, let B = B else {
+            return false
+        }
+        return dfs(A, B) || isSubStructure(A.left, B) || isSubStructure(A.right, B)
+    }
+
+    private func dfs(_ A: TreeNode?, _ B: TreeNode?) -> Bool {
+        if B == nil {
+            return true
+        }
+        guard let A = A else {
+            return false
+        }
+        if A.val != B!.val {
+            return false
+        }
+        return dfs(A.left, B?.left) && dfs(A.right, B?.right)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题26. 树的子结构/Solution.swift

@@ -0,0 +1,33 @@
+/* public class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+* }
+*/
+
+class Solution {
+    func isSubStructure(_ A: TreeNode?, _ B: TreeNode?) -> Bool {
+        guard let A = A, let B = B else {
+            return false
+        }
+        return dfs(A, B) || isSubStructure(A.left, B) || isSubStructure(A.right, B)
+    }
+
+    private func dfs(_ A: TreeNode?, _ B: TreeNode?) -> Bool {
+        if B == nil {
+            return true
+        }
+        guard let A = A else {
+            return false
+        }
+        if A.val != B!.val {
+            return false
+        }
+        return dfs(A.left, B?.left) && dfs(A.right, B?.right)
+    }
+}