Detailed illustration of the four types of traversal of binary trees (pre-order, in-order, and post-order hierarchical traversal)

In this paper, take this binary tree as an example

1. Preorder traversal

normal operation

root first, then left, then right

The overall structure of the traversal is determined:

Determines the overall structure in the left subtree

Proceed to:

At this point, the traversal in the left subtree has been completed

Determine the overall structure in the right subtree

The preamble ends and
the result is: ABDFECGIJHK

easy way

Start from the root node and go around the binary tree to the left, the order of the nodes passed is the pre-order traversal order

The result is: ABDFECGIJHK

2. Inorder traversal

normal operation

First left, then root, then right

From this, it can be determined that the root A is in the middle, and the order in the left and right subtrees is respectively determined below

In the left subtree:

This determines the order in the left subtree

In the right subtree:
divide the right subtree as a whole

So it can be determined:

continue:

End of inorder traversal
The result is: FDBEAIGJCHK

easy way

Take this binary tree as an example

The result is: FDBEAIGJCHK

3. Post-order traversal

normal operation

first left, then right, then root

Separate the overall structure, and the root node will always be at the last position during post-order traversal

Continue to divide the structure of the left subtree

Since then, the traversal in the left subtree ends

Divide the right subtree structure

end of postorder traversal

The result is: FDEBIJGKHCA

Four. Hierarchical traversal

normal operation

Take each line of the binary tree as a whole, output from top to bottom, and output each line in order from left to right The

first line: A
The second line: BC
The third line: DEGH
The fourth line: FIJK
The result is: ABCDEGHFIJK