feat: add swift implementation to lcof2 problem: No.056 (doocs#3085)

Author: klever34

lcof2/剑指 Offer II 056. 二叉搜索树中两个节点之和/README.md

@@ -208,6 +208,52 @@ function find(root: TreeNode | null, k: number, nodes: Set<number>): boolean {
 }
 ```
 
+#### Swift
+
+```swift
+/* class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+*     init() {
+*         self.val = 0
+*         self.left = nil
+*         self.right = nil
+*     }
+*     init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+*     init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+*         self.val = val
+*         self.left = left
+*         self.right = right
+*     }
+* }
+*/
+
+class Solution {
+    private var nodes: Set<Int> = []
+
+    func findTarget(_ root: TreeNode?, _ k: Int) -> Bool {
+        nodes = []
+        return find(root, k)
+    }
+
+    private func find(_ root: TreeNode?, _ k: Int) -> Bool {
+        guard let node = root else {
+            return false
+        }
+        if nodes.contains(k - node.val) {
+            return true
+        }
+        nodes.insert(node.val)
+        return find(node.left, k) || find(node.right, k)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 056. 二叉搜索树中两个节点之和/Solution.swift

@@ -0,0 +1,41 @@
+/* class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+*     init() {
+*         self.val = 0
+*         self.left = nil
+*         self.right = nil
+*     }
+*     init(_ val: Int) {
+*         self.val = val
+*         self.left = nil
+*         self.right = nil
+*     }
+*     init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+*         self.val = val
+*         self.left = left
+*         self.right = right
+*     }
+* }
+*/
+
+class Solution {
+    private var nodes: Set<Int> = []
+
+    func findTarget(_ root: TreeNode?, _ k: Int) -> Bool {
+        nodes = []
+        return find(root, k)
+    }
+
+    private func find(_ root: TreeNode?, _ k: Int) -> Bool {
+        guard let node = root else {
+            return false
+        }
+        if nodes.contains(k - node.val) {
+            return true
+        }
+        nodes.insert(node.val)
+        return find(node.left, k) || find(node.right, k)
+    }
+}