Python实现二叉树的常见遍历操作总结【7种方法】

class TreeNode:
  def __init__(self, x):
    self.val = x
    self.left = None
    self.right = None

def preorder(root,res=[]):
  if not root:
    return 
  res.append(root.val)
  preorder(root.left,res)
  preorder(root.right,res)
  return res

def preorder(root):
  res=[]
  if not root: 
    return []
  stack=[root]
  while stack:
    node=stack.pop()
    res.append(node.val)
    if node.right:
      stack.append(node.right)
    if node.left:
      stack.append(node,left)
  return res

def inorder(root,res=[]):
  if not root:
    return 
  inorder(root.left,res)
  res.append(root.val)
  inorder(root.right,res)
  return res

def inorder(root):
  stack=[]
  node=root
  res=[]
  while stack or node:
    while node:
      stack.append(node)
      node=node.left
    node=stack.pop()
    res.append(node.val)
    node=node.right
  return res

def laorder(root,res=[]):
  if not root:
    return 
  laorder(root.left,res)
  laorder(root.right,res)
  res.append(root.val)
  return res

def laorder(root):
  stack=[root]
  res=[]
  while stack:
    node=stack.pop()
    if node.left:
      stack.append(node.left)
    if node.right:
      stack.append(node.right)
    res.append(node.val)
  return res[::-1]

def levelorder(root):
  queue=[root]
  res=[]
  while queue:
    node=queue.pop(0)
    if node.left: 
      queue.append(node.left)
    if node.right:
      queue.append(node.right)
    res.append(node.val)
  return res