feat: add swift implementation to lcof2 problem: No.054 (doocs#3083)

Author: klever34

lcof2/剑指 Offer II 054. 所有大于等于节点的值之和/README.md

@@ -317,6 +317,51 @@ var convertBST = function (root) {
 };
 ```
 
+#### 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 s = 0
+
+    func convertBST(_ root: TreeNode?) -> TreeNode? {
+        dfs(root)
+        return root
+    }
+
+    private func dfs(_ root: TreeNode?) {
+        guard let node = root else {
+            return
+        }
+        dfs(node.right)
+        s += node.val
+        node.val = s
+        dfs(node.left)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 054. 所有大于等于节点的值之和/Solution.swift

@@ -0,0 +1,40 @@
+/* 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 s = 0
+
+    func convertBST(_ root: TreeNode?) -> TreeNode? {
+        dfs(root)
+        return root
+    }
+
+    private func dfs(_ root: TreeNode?) {
+        guard let node = root else {
+            return
+        }
+        dfs(node.right)
+        s += node.val
+        node.val = s
+        dfs(node.left)
+    }
+}