被網(wǎng)上各種寫法惡心到了酗失，下面是一個統(tǒng)一寫法。
只要了解了先序遍歷昧绣，中序和后序遍歷都懂了规肴。
這里面用到了棧，用棧不斷壓入根夜畴、左孩子拖刃，通過pop來回溯父節(jié)點，再訪問右孩子贪绘。
- 先序遍歷
"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
"""
@param root: The root of binary tree.
@return: Postorder in ArrayList which contains node values.
"""
result = []
def preorderTraversal(self, root):
# write your code here
if root is None:
return []
stack = []
seq = [] #記錄先序訪問序列
while ((root!=None) | (len(stack)!=0)):
if root!=None:
seq.append(root.val) #先訪問根節(jié)點
stack.append(root)
root = root.left
else:
root = stack.pop() #回溯至父節(jié)點
root = root.right
return seq
- 中序遍歷
"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
"""
@param root: The root of binary tree.
@return: Postorder in ArrayList which contains node values.
"""
result = []
def inorderTraversal(self, root):
# write your code here
if root is None:
return []
stack = []
seq = []
output = []
while ((root!=None) | (len(stack)!=0)):
if root!=None:
stack.append(root)
root = root.left
else:
root = stack.pop()
seq.append(root.val) # 左孩子先pop出來兑牡，再pop根節(jié)點
root = root.right
return seq
- 后序遍歷
先序：根左右
后續(xù)：左右根
即把先序順序中的 ‘根左右’轉(zhuǎn)換為‘根右左’，然后反過來就變成了‘左右根’税灌。
"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
"""
@param root: The root of binary tree.
@return: Postorder in ArrayList which contains node values.
"""
result = []
def postorderTraversal(self, root):
# write your code here
if root is None:
return []
stack = []
seq = []
output = []
while ((root!=None) | (len(stack)!=0)):
if root!=None:
seq.append(root.val)
stack.append(root)
root = root.right # 這從left變成了 right
else:
root = stack.pop()
root = root.left # 這從right變成了 left
while seq: # 后序遍歷 是 將先序遍歷的反過來
output.append(seq.pop())
return output
