添加 0617.合并二叉树.md Scala版本

problems/0617.合并二叉树.md

@@ -631,7 +631,60 @@ function mergeTrees(root1: TreeNode | null, root2: TreeNode | null): TreeNode |
 };
 ```
 
+## Scala
 
+递归:
+```scala
+object Solution {
+  def mergeTrees(root1: TreeNode, root2: TreeNode): TreeNode = {
+    if (root1 == null) return root2 // 如果root1为空，返回root2
+    if (root2 == null) return root1 // 如果root2为空，返回root1
+    // 新建一个节点，值为两个节点的和
+    var node = new TreeNode(root1.value + root2.value)
+    // 往下递归
+    node.left = mergeTrees(root1.left, root2.left)
+    node.right = mergeTrees(root1.right, root2.right)
+    node // 返回node，return关键字可以省略
+  }
+}
+```
+
+迭代:
+```scala
+object Solution {
+  import scala.collection.mutable
+  def mergeTrees(root1: TreeNode, root2: TreeNode): TreeNode = {
+    if (root1 == null) return root2
+    if (root2 == null) return root1
+    var stack = mutable.Stack[TreeNode]()
+    // 先放node2再放node1
+    stack.push(root2)
+    stack.push(root1)
+    while (!stack.isEmpty) {
+      var node1 = stack.pop()
+      var node2 = stack.pop()
+      node1.value += node2.value
+      if (node1.right != null && node2.right != null) {
+        stack.push(node2.right)
+        stack.push(node1.right)
+      } else {
+        if(node1.right == null){
+          node1.right = node2.right
+        }
+      }
+      if (node1.left != null && node2.left != null) {
+        stack.push(node2.left)
+        stack.push(node1.left)
+      } else {
+        if(node1.left == null){
+          node1.left = node2.left
+        }
+      }
+    }
+    root1
+  }
+}
+```
 
 
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