@@ -591,6 +591,80 @@ function postorderTraversal(root: TreeNode | null): number[] {
591591 return res ;
592592};
593593```
594+ Scala:
595+ ``` scala
596+ // 前序遍历
597+ object Solution {
598+ import scala .collection .mutable
599+ def preorderTraversal (root : TreeNode ): List [Int ] = {
600+ val res = mutable.ListBuffer [Int ]()
601+ val stack = mutable.Stack [TreeNode ]()
602+ if (root != null ) stack.push(root)
603+ while (! stack.isEmpty) {
604+ var curNode = stack.top
605+ if (curNode != null ) {
606+ stack.pop()
607+ if (curNode.right != null ) stack.push(curNode.right)
608+ if (curNode.left != null ) stack.push(curNode.left)
609+ stack.push(curNode)
610+ stack.push(null )
611+ } else {
612+ stack.pop()
613+ res.append(stack.pop().value)
614+ }
615+ }
616+ res.toList
617+ }
618+ }
619+ 620+ // 中序遍历
621+ object Solution {
622+ import scala .collection .mutable
623+ def inorderTraversal (root : TreeNode ): List [Int ] = {
624+ val res = mutable.ListBuffer [Int ]()
625+ val stack = mutable.Stack [TreeNode ]()
626+ if (root != null ) stack.push(root)
627+ while (! stack.isEmpty) {
628+ var curNode = stack.top
629+ if (curNode != null ) {
630+ stack.pop()
631+ if (curNode.right != null ) stack.push(curNode.right)
632+ stack.push(curNode)
633+ stack.push(null )
634+ if (curNode.left != null ) stack.push(curNode.left)
635+ } else {
636+ // 等于空的时候好办,弹出这个元素
637+ stack.pop()
638+ res.append(stack.pop().value)
639+ }
640+ }
641+ res.toList
642+ }
643+ }
594644
645+ // 后序遍历
646+ object Solution {
647+ import scala .collection .mutable
648+ def postorderTraversal (root : TreeNode ): List [Int ] = {
649+ val res = mutable.ListBuffer [Int ]()
650+ val stack = mutable.Stack [TreeNode ]()
651+ if (root != null ) stack.push(root)
652+ while (! stack.isEmpty) {
653+ var curNode = stack.top
654+ if (curNode != null ) {
655+ stack.pop()
656+ stack.push(curNode)
657+ stack.push(null )
658+ if (curNode.right != null ) stack.push(curNode.right)
659+ if (curNode.left != null ) stack.push(curNode.left)
660+ } else {
661+ stack.pop()
662+ res.append(stack.pop().value)
663+ }
664+ }
665+ res.toList
666+ }
667+ }
668+ ```
595669-----------------------
596670<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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