Python implements a two-fork tree traversal

A binary tree is a set of finite elements that are either empty or have an element called the root node (root) and two disjoint, respectively, two-tree trees that are called Saozi right subtrees.

• Each node of a binary tree has a maximum of two subtrees trees (no nodes with a degree greater than 2), and the subtree of the binary tree has left and right points, and the order cannot be reversed.
• The first layer of the binary tree has a maximum of 2^{i-1} nodes.
• The two-fork tree with a depth of K has at most 2^k-1 nodes;
• For any binary tree T, if its terminal node number is N0, the number of nodes with a degree of 2 is N2, then n0=n2+1

First build a binary tree:

1 class Node:   2     def __init__ (self,value=none,left=none,right=None):   3         self.value=value  4         self.left=left    # left dial hand tree 5         Self.right=right  # Right sub-tree

The following gives the pre-sequence traversal/middle sequence traversal/post-order traversal of a two-fork tree

1 defPretraverse (Root):2     " "3 Pre-sequence traversal4     " "5     ifroot==None:6         return  7     Print(Root.value)8 pretraverse (root.left)9 pretraverse (root.right)Ten  One defMidtraverse (Root): A     " " - Middle Sequence Traversal -     " " the     ifroot==None: -         return   - midtraverse (root.left) -     Print(Root.value) + midtraverse (root.right) -    + defAftertraverse (Root): A     " " at Post-post traversal -     " " -     ifroot==None: -         return   - aftertraverse (root.left) - aftertraverse (root.right) in     Print(Root.value)

An example is given below to verify the program

1 if __name__=='__main__':2Root=node ('D', Node ('B', Node ('A'), Node ('C')), Node ('E', Right=node ('G', Node ('F'))))3     Print('Pre-order traversal:')4 Pretraverse (Root)5     Print('\ n')6     Print('Middle sequence Traversal:')7 Midtraverse (Root)8     Print('\ n')9     Print('Post-post traversal:')Ten Aftertraverse (Root) One     Print('\ n')

The result of the output is

Pre-sequence traversal: DBACEGF sequence Traversal: ABCDEFG post-order traversal: acbfged

So, if we know the binary tree's pre-sequence traversal and the middle sequence traversal, we ask the second-order traversal of the binary tree

1Prelist = List ('12473568')2Midlist = List ('47215386')3Afterlist = []4 5 defFindtree (prelist, Midlist, afterlist):6     ifLen (prelist) = =0:7         return8     ifLen (prelist) = = 1:9 afterlist.append (prelist[0])Ten         return OneRoot =Prelist[0] An =Midlist.index (Root) -Findtree (prelist[1:n + 1], midlist[:n], afterlist) -Findtree (Prelist[n + 1:], Midlist[n + 1:], afterlist) theAfterlist.append (Root)

The result is:

 [ " 7  "  ,  4  "  ,  2  "  ,  5  "  ,  8  "  ,  6  "  ,  3  "  ,  1  "  ]

1 if the preceding sequence: DBACEGF and middle order: ABCDEFG, the results are: 2 ['A''C''B'  'F'G'E'  D']

Python implements traversal of a two-fork tree