Leetcode: Binary Tree Preorder Traversal @Python

Iterative solution:

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param root, a tree node
    # @return a list of integers
    def preorderTraversal(self, root):
        prelist=[]
        rst=[]
        if root==None:
            return rst
        prelist.append(root)
        while(prelist):
            crt=prelist.pop()
            rst.append(crt.val)
            if crt.right:
                prelist.append(crt.right)
            if crt.left:
                prelist.append(crt.left)
        return rst

Recursive solution:

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param root, a tree node
    # @return a list of integers
    def preorderecur(self, root, rst):
        if not root: return
        rst.append(root.val)
        self.preorderecur(root.left,rst)
        self.preorderecur(root.right,rst)
        return
    def preorderTraversal(self, root):
        rst=[]
        self.preorderecur(root,rst)
        return rst