144. Binary Tree Preorder Traversal 先序遍历二叉树

Given a binary tree, return the preorder traversal of its nodes' values.

For example:
Given binary tree [1,null,2,3],

   1
    \
     2
    /
   3

return [1,2,3].

Note: Recursive solution is trivial, could you do it iteratively?

1. # Definition for a binary tree node.
2. # class TreeNode:
3. # def __init__(self, x):
4. # self.val = x
5. # self.left = None
6. # self.right = None
8. class Solution:
9. def preorderTraversal(self, root):
10. """
11. :type root: TreeNode
12. :rtype: List[int]
13. """
14. res = []
15. stack = [root]
16. while stack and stack[0]:
17. node = stack.pop()
18. res.append(node.val)
19. if node.right:
20. stack.append(node.right)
21. if node.left:
22. stack.append(node.left)
23. return res

来自为知笔记(Wiz)

转载于:https://www.cnblogs.com/xiejunzhao/p/8419844.html