原题
给定一个 N 叉树,返回其节点值的前序遍历。
例如,给定一个 3叉树
:
返回其前序遍历: [1,3,5,6,2,4]
。
说明: 递归法很简单,你可以使用迭代法完成此题吗?
class Solution {public List<Integer> preorder(Node root) {List<Integer> list = new ArrayList<>();if(root == null){return list;}list.add(root.val);List<Node> children = root.children;if(children!=null){for(Node child : children){list.addAll(preorder(child));}}return list;}}
class Solution {public List<Integer> preorder(Node root) {List<Integer> list = new ArrayList<>();if(root == null){return list;}LinkedList<Node> stack = new LinkedList<>();stack.push(root);while(!stack.isEmpty()){root = stack.pop();list.add(root.val);List<Node> children = root.children;if(children!=null){for(int i = children.size() - 1;i >= 0;i--){stack.push(children.get(i));}}}return list;}}