Given a binary tree, return the preorder traversal of its nodes‘ values.
Example:
Input:[1,null,2,3]1 2 / 3 Output:[1,2,3]
Follow up: Recursive solution is trivial, could you do it iteratively?
# Definition for a binary tree node. # class TreeNode(object): # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution(object): def preorderTraversal(self, root): """ :type root: TreeNode :rtype: List[int] """ res = [] stack = [root] while stack: top = stack.pop() if top: res.append(top.val) stack.append(top.right) stack.append(top.left) return res
144. Binary Tree Preorder Traversal
原文：https://www.cnblogs.com/boluo007/p/12441412.html