添加 Swift 代码实现

animation-simulation/二叉树/二叉树的前序遍历(栈).md

@@ -67,3 +67,32 @@ class Solution {
 }
 ```
 
+Swift Code：
+
+```swift
+class Solution {
+
+    func preorderTraversal(_ root: TreeNode?) -> [Int] {
+        var list:[Int] = []
+        var stack:[TreeNode] = []
+
+        guard root != nil else {
+            return list
+        }
+        stack.append(root!)
+        while !stack.isEmpty {
+            let temp = stack.popLast()
+            if let right = temp?.right {
+                stack.append(right)
+            }
+            if let left = temp?.left {
+                stack.append(left)
+            }
+            //这里也可以放到前面
+            list.append((temp?.val)!)
+        }
+        return list
+    }
+}
+```
+