Python algorithm-two fork tree depth first traversal

Two fork Tree

Composition

1. root node BinaryTree:Root

2, each node, have left dial hand node and right child node (can be empty) TreeNode:value,left, Right

Traversal of a binary tree:

Traverse binary Tree: Depth-first traversal, breadth-first traversal.

breadth: Traverse sibling nodes first, then traverse child nodes

Depth: traverse the child nodes first, then traverse the sibling nodes

depth Traversal result:50/20/60/15/30/70

breadth Traversal result:50/20/15/30/60/70

The depth traversal is divided into the first order, the middle order, the sequential traversal mode:

First Order traversal: first root node, then left subtree, then right sub-tree

First Order traversal result:50/20/15/30/60/70

Middle sequence traversal: First left subtree, then root node, then right sub-tree

Middle Sequence traversal result:15/20/30/50/60/70

Post-post traversal: First left subtree, then right subtree, then root node

Post-post traversal result:15/30/20/70/60/50

Code implementation:

# Encoding=utf-8

Class TreeNode (object): # defines a binary tree class

def __init__ (Self,val,left=none,right=none):

Self.val = Val

Self.left = Left

Self.right = Right

Class BinaryTree (object):

def __init__ (Self,root=none):

Self.root = root

Def prescan (self,retlist, node): # Sequence traversal: First, then left, then right

IF node! = None:

Retlist.append (Node.val)

Self.prescan (Retlist, Node.left)

Self.prescan (Retlist, Node.right)

Return retlist

def midscan (self, Retlist, node): # Middle sequence traversal: first left, back, right

IF node! = None:

Self.midscan (Retlist, Node.left)

Retlist.append (Node.val)

Self.midscan (Retlist, Node.right)

Return retlist

def postscan (self, Retlist, node): # post- traversal: First left, then right, followed by

IF node! = None:

Self.postscan (Retlist, Node.left)

Self.postscan (Retlist, Node.right)

Retlist.append (Node.val)

Return retlist

if __name__ = = ' __main__ ':

root = TreeNode (50)

Root.left = TreeNode (20,left=treenode), Right=treenode (30,right=treenode (12)))

Root.right = TreeNode (60,right=treenode (70))

BTree = BinaryTree (Root)

Retlist = Btree.prescan ([],btree.root)

Print Retlist

RetList2 = Btree.midscan ([],btree.root)

Print RetList2

RETLIST3 = Btree.postscan ([],btree.root)

Print RetList3

Python algorithm-two fork tree depth first traversal