Merge pull request #1922 from sonjh1217/main

[sonjh1217] WEEK 10 Solutions

Author: TonyKim9401

invert-binary-tree/sonjh1217.swift

@@ -0,0 +1,41 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init() { self.val = 0; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+ *         self.val = val
+ *         self.left = left
+ *         self.right = right
+ *     }
+ * }
+ */
+class Solution {
+    func invertTree(_ root: TreeNode?) -> TreeNode? {
+        guard var invertedRoot = root else {
+            return nil
+        }
+
+        func invert(node: TreeNode?) -> TreeNode? {
+            guard var node = node else {
+                return nil
+            }
+
+            if node.left == nil
+            && node.right == nil {
+                return node
+            }
+
+            let left = node.left
+            node.left = invert(node: node.right)
+            node.right = invert(node: left)
+            return node
+        }
+
+        return invert(node: invertedRoot)
+    }
+}
+