[数据结构]二叉树-前序遍历-递归与非递归

# 二叉树前序遍历(非递归)
class TreeNode:
    def __init__(self,val):
        self.data=val
        self.left=None
        self.right=None
def  preorder_travel(root):
    if root is None:
        return []
    
    stack=[root]
    result=[]

    while stack:
        node=stack.pop()
        result.append(node.data)
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)

    return result

#二叉树前序遍历(递归)
def simple_travel(root):
    result=[]
    if root==None:
        return []
    else:
        return [root.data]+simple_travel(root.left)+simple_travel(root.right)

    return result

#测试代码
head=TreeNode(1)
head.right=TreeNode(3)
head.left=TreeNode(2)
head.left.left=TreeNode(4)
head.left.right=TreeNode(5)

print(preorder_travel(head))
print(simple_travel(head))