从上到下打印出二叉树的每个节点,同一层的节点按照从左到右的顺序打印。
例如:
给定二叉树: [3,9,20,null,null,15,7]
返回:[3,9,20,15,7]
=============队列=============
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def levelOrder(self, root: TreeNode) -> List[int]: if not root: return [] from collections import deque q = deque() q.append(root) res = [] while q: cur = q.popleft() res.append(cur.val) if cur.left: q.append(cur.left) if cur.right: q.append(cur.right) return res
从上到下按层打印二叉树,同一层的节点按从左到右的顺序打印,每一层打印到一行。
例如:
给定二叉树: [3,9,20,null,null,15,7]
,
返回其层次遍历结果:
[
[3],
[9,20],
[15,7]
]
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] from collections import deque q = deque() q.append(root) ans = [] while q: tmp = deque() res = [] while q: cur = q.popleft() res.append(cur.val) if cur.left: tmp.append(cur.left) if cur.right: tmp.append(cur.right) q = tmp ans.append(res) return ans
请实现一个函数按照之字形顺序打印二叉树,即第一行按照从左到右的顺序打印,第二层按照从右到左的顺序打印,第三行再按照从左到右的顺序打印,其他行以此类推。
例如:
给定二叉树: [3,9,20,null,null,15,7],
返回其层次遍历结果:
[
[3],
[20,9],
[15,7]
]
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] from collections import deque q = deque() q.append(root) ans = [] flag = 1 while q: tmp = deque() res = [] while q: cur = q.popleft() res.append(cur.val) if cur.left: tmp.append(cur.left) if cur.right: tmp.append(cur.right) q = tmp if flag == 1: ans.append(res) else: ans.append(res[::-1]) flag = -flag return ans