题解 | #二叉树的前序遍历#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
#
# @param root TreeNode类
# @return int整型一维数组
#
class Solution:
    def preorderTraversal(self, root: TreeNode) -> List[int]:
        # res records the values
        # tmp records the current branch(path)
        # cur search through this tree
        res, tmp, cur = [], [], root

        # when searcher or tmp is not None
        while cur or tmp:
            # record the cur path to tmp
            # add current val
            # move the the left child
            while cur:
                tmp += [cur]
                res += [cur.val]
                cur = cur.left
            # back to the parent branch
            # search right side
            cur = tmp.pop()
            cur = cur.right
        return res