题解 | #两种思路# #二叉树的前序遍历#

#coding:utf-8
# 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 __init__(self):
        self.path = []

    def preorderTraversal(self , root ):
        # write code here
        #self.dfs(root)
        self.byStack(root)
        print ("path: ", self.path)
        return self.path
    
    def byStack(self, root):
        if root == None:
            return 
        stack = []
        stack.append(root)

        while len(stack) > 0: 
            cur = stack.pop()
            self.path.append(cur.val)
            if cur.right != None:
                stack.append(cur.right)
            if cur.left != None:
                stack.append(cur.left)

        return 

    def dfs(self, root):
        if root == None:
            return 
        self.path.append(root.val)
        self.dfs(root.left)
        self.dfs(root.right)
        return