添加 二叉树理论基础篇 Swift版本

problems/二叉树理论基础.md

@@ -227,6 +227,21 @@ function TreeNode(val, left, right) {
 }
 ```
 
+Swift:
+```Swift
+class TreeNode<T> {
+    var value: T
+    var left: TreeNode?
+    var right: TreeNode?
+    init(_ value: T,
+         left: TreeNode? = nil,
+         right: TreeNode? = nil) {
+        self.value = value
+        self.left = left
+        self.right = right
+    }
+}
+```
 
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