怎么用Python递归式实现二叉树前序,中序,后序遍历
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摘要： 记忆点：前序：VLR中序：LVR后序：LRV举例：一颗二叉树如下图所示：则它的前序、中序、后序遍历流程如下图所示：1.前序遍历classSolution:defpreorderTraversal(self,root:TreeNode):defpreorder(root:TreeNode):ifnotroot:returnres.append(root... ...
音频解说
目录
(为您整理了一些要点),点击可以直达。记忆点：
前序：VLR
中序：LVR
后序：LRV
举例：
一颗二叉树如下图所示：
则它的前序、中序、后序遍历流程如下图所示：
1.前序遍历
classSolution:defpreorderTraversal(self,root:TreeNode):defpreorder(root:TreeNode):ifnotroot:returnres.append(root.val)preorder(root.left)preorder(root.right)res=[]preorder(root)returnres
2.中序遍历
classSolution:definorderTraversal(self,root:TreeNode):definorder(root:TreeNode):ifnotroot:returninorder(root.left)res.append(root.val)inorder(root.right)res=[]inorder(root)returnres
3.后序遍历
classSolution:defpostorderTraversal(self,root:TreeNode):defpostorder(root:TreeNode):ifnotroot:returnpostorder(root.left)res.append(root.val)postorder(root.right)res=[]postorder(root)returnres
4.测试
classTreeNode:def__init__(self,val=0,left=None,right=None):self.val=valself.left=leftself.right=right#用列表递归创建二叉树defcreateTree(root,list_n,i):ifi<len(list_n):iflist_n[i]=='null':returnNoneelse:root=TreeNode(val=list_n[i])root.left=createTree(root.left,list_n,2*i+1)root.right=createTree(root.right,list_n,2*i+2)returnrootreturnrootclassSolution:defpreorderTraversal(self,root:TreeNode):#前序defpreorder(root:TreeNode):ifnotroot:returnres.append(root.val)preorder(root.left)preorder(root.right)res=[]preorder(root)returnresdefinorderTraversal(self,root:TreeNode):#中序definorder(root:TreeNode):ifnotroot:returninorder(root.left)res.append(root.val)inorder(root.right)res=[]inorder(root)returnresdefpostorderTraversal(self,root:TreeNode):#后序defpostorder(root:TreeNode):ifnotroot:returnpostorder(root.left)postorder(root.right)res.append(root.val)res=[]postorder(root)returnresif__name__=="__main__":root=TreeNode()list_n=[1,2,3,4,5,6,7,8,'null',9,10]root=createTree(root,list_n,0)s=Solution()res_pre=s.preorderTraversal(root)res_in=s.inorderTraversal(root)res_post=s.postorderTraversal(root)print(res_pre)print(res_in)print(res_post)
5.结果
6.补充
6.1N叉树前序遍历
"""#DefinitionforaNode.classNode:def__init__(self,val=None,children=None):self.val=valself.children=children"""classSolution:defpostorder(self,root:'Node')->List[int]:defseq(root):ifnotroot:returnres.append(root.val)forchildinroot.children:seq(child)res=[]seq(root)returnresN叉树后序遍历"""#DefinitionforaNode.classNode:def__init__(self,val=None,children=None):self.val=valself.children=children"""classSolution:defpostorder(self,root:'Node')->List[int]:defseq(root):ifnotroot:returnforchildinroot.children:seq(child)res.append(root.val)res=[]seq(root)returnres
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