Recursive and non-recursive python implementations of binary tree First order, middle sequence, post-order traversal

1. First Order traversal: the right subtree, left dial hand tree, root node

1 # Sequential Print binary tree (recursive) 2 def preordertraverse (node): 3     if  is None: 4         return None 5     Print (Node.val) 6     preordertraverse (node.left)7     preordertraverse (node.right)

1 #Sequential Print binary tree (non-recursive)2 defPreordertravese (node):3stack =[node]4      whileLen (Stack) >0:5         Print(Node.val)6         ifNode.right is  notNone:7 stack.append (node.right)8         ifNode.left is  notNone:9 stack.append (node.left)Tennode = Stack.pop ()

2. Middle Sequence traversal: the right subtree, the root node, left dial hand tree

1 # middle order Print binary tree (recursive) 2 def inordertraverse (node): 3     if  is None: 4         return None 5     inordertraverse (node.left)6     Print (Node.val) 7     Inordertraverse (Node.right)

1 #middle order Print binary tree (non-recursive)2 definordertraverse (node):3stack =[node]4pos =node5      whilePos is  notNoneorLen (Stack) >0:6         ifPos is  notNone:7 stack.append (POS)8pos =Pos.left9         Else:Tenpos =Stack.pop () One             Print(Pos.val) Apos = Pos.right

3. Post-post traversal: root node, right subtree, left dial hand tree

1 # Post -Secondary print binary tree (recursive) 2 def postordertraverse (node): 3     if  is None: 4         return None 5     postordertraverse (node.left)6    postordertraverse (node.right)7      Print(node.val)

1 #Post -Secondary printing binary tree (non-recursive)2 #use two stack structures3 #first stack in stack order: left node, right node, and node4 #First Stack popup order: Left node, right node, and node (first sequence traversal stack popup order: left-to-right)5 #the second stack is stored for each popup in the first stack, followed by a stack6 #Finally, the second stack is out of the stack .7 defpostordertraverse (node):8stack =[node]9Stack2 = []Ten      whileLen (Stack) >0: Onenode =Stack.pop () A stack2.append (node) -         ifNode.left is  notNone: - stack.append (node.left) the         ifNode.right is  notNone: - stack.append (node.right) -      whileLen (Stack2) >0: -         Print(Stack2.pop (). val)

4. Traverse by layer: from top to bottom, left to right, by layer

1 #Advanced first-out selection queue structure2 ImportQueue3 defLayertraverse (head):4     if  notHead:5         returnNone6que = queue. Queue ()#Create a FIFO queue7 Que.put (head)8      while  notque.empty ():9Head = Que.get ()#pops up the first element and printsTen         Print(Head.val) One         ifHead.left:#If the node has a left child node, join the queue (push the left node first) A que.put (head.left) -         ifHead.right:#If the node has a right child node, join the queue (then push the right node) -Que.put (Head.right)

5. Number of two fork tree nodes

1 # finding the number of two-fork tree nodes 2 def treenodenums (node): 3     if  is None: 4         return 0 5     Nums = treenodenums (node.left)6     nums + = treenodenums (node.right)7     return nums + 1

6. Maximum depth of two-fork tree

1 # two maximum depth of the fork tree 2 def btreedepth (node): 3     if  is None: 4         return 0 5     Ldepth = btreedepth (node.left)6     rdepth = btreedepth (node.right)7     return (Max (ldepth, rdepth) + 1)

Recursive and non-recursive python implementations of binary tree First order, middle sequence, post-order traversal