binary_tree_postorder_traversal
binary_tree_postorder_traversal.py 源码
# 二叉树的后序遍历
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
class Solution:
# 递归
def postorderTraversal_1(self, root: TreeNode) -> List[int]:
def dfs(node, res):
if node:
dfs(node.left, res)
dfs(node.right, res)
res.append(node.val)
res = []
dfs(root, res)
return res
# 迭代
def postorderTraversal_2(self, root: TreeNode) -> List[int]:
if not root:
return []
stack, res = [root], []
while len(stack) > 0:
node = stack.pop()
res.insert(0, node.val)
if node.left:
stack.append(node.left)
if node.right:
stack.append(node.right)
return res
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