@@ -568,6 +568,71 @@ func inorderTraversal(_ root: TreeNode?) -> [Int] {
568568 return result
569569}
570570```
571+ Scala:
572+ ``` scala
573+ // 前序遍历(迭代法)
574+ object Solution {
575+ import scala .collection .mutable
576+ def preorderTraversal (root : TreeNode ): List [Int ] = {
577+ val res = mutable.ListBuffer [Int ]()
578+ if (root == null ) return res.toList
579+ // 声明一个栈,泛型为TreeNode
580+ val stack = mutable.Stack [TreeNode ]()
581+ stack.push(root) // 先把根节点压入栈
582+ while (! stack.isEmpty) {
583+ var curNode = stack.pop()
584+ res.append(curNode.value) // 先把这个值压入栈
585+ // 如果当前节点的左右节点不为空,则入栈,先放右节点,再放左节点
586+ if (curNode.right != null ) stack.push(curNode.right)
587+ if (curNode.left != null ) stack.push(curNode.left)
588+ }
589+ res.toList
590+ }
591+ }
571592
593+ // 中序遍历(迭代法)
594+ object Solution {
595+ import scala .collection .mutable
596+ def inorderTraversal (root : TreeNode ): List [Int ] = {
597+ val res = mutable.ArrayBuffer [Int ]()
598+ if (root == null ) return res.toList
599+ val stack = mutable.Stack [TreeNode ]()
600+ var curNode = root
601+ // 将左节点都入栈,当遍历到最左(到空)的时候,再弹出栈顶元素,加入res
602+ // 再把栈顶元素的右节点加进来,继续下一轮遍历
603+ while (curNode != null || ! stack.isEmpty) {
604+ if (curNode != null ) {
605+ stack.push(curNode)
606+ curNode = curNode.left
607+ } else {
608+ curNode = stack.pop()
609+ res.append(curNode.value)
610+ curNode = curNode.right
611+ }
612+ }
613+ res.toList
614+ }
615+ }
616+ 617+ // 后序遍历(迭代法)
618+ object Solution {
619+ import scala .collection .mutable
620+ def postorderTraversal (root : TreeNode ): List [Int ] = {
621+ val res = mutable.ListBuffer [Int ]()
622+ if (root == null ) return res.toList
623+ val stack = mutable.Stack [TreeNode ]()
624+ stack.push(root)
625+ while (! stack.isEmpty) {
626+ val curNode = stack.pop()
627+ res.append(curNode.value)
628+ // 这次左节点先入栈,右节点再入栈
629+ if (curNode.left != null ) stack.push(curNode.left)
630+ if (curNode.right != null ) stack.push(curNode.right)
631+ }
632+ // 最后需要翻转List
633+ res.reverse.toList
634+ }
635+ }
636+ ```
572637-----------------------
573638<div align =" center " ><img src =https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width =500 > </img ></div >
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