两种遍历方式
广度优先遍历和深度优先遍历，都可用递归和非递归实现
定义二叉树
class Node:def __init__(self, root):self.root = rootself.left = Noneself.right = None
递归
# depth-first-traversal# pre-orderdef pre_order(tree):print(tree.root)pre_order(tree.left)pre_order(tree.right)# mid-orderdef mid-order(tree):mid-order(tree.left)print(tree.root)mid-order(tree.right)# post-orderdef post_order(tree):post_order(tree.left)post_order(tree.right)print(tree.root)# breadth-first-traversal
非递归
# depth-first-traversal# pre-orderdef pre_order(tree):stack = [tree]while stack:print(tree.val)if tree.right:stack.append(tree.right)if tree.left:stack.append(tree.left)tree = stack.pop() # mid-order# post-order# breadth-first-traversaldef bft(tree):stack = [tree]while stack:t = stack.pop()if isinstance(t, Node):if t.right:stack.append(t.right)if t.left:stack.append(t.left)stack.append(t.val)else:print(t)
leetcode原题：leetcode 层次遍历
ref
ref1
