Interview Road (one)-java recursive and non-recursive binary tree pre-order traversal

Traversal of a binary tree

The most important and basic operation for a binary tree is traversal.
Traversing a binary tree means accessing each node in a binary tree in a certain order. The so-called access node refers to the node for various operations of the abbreviation. For example, querying the contents of a Node data field, or outputting its value, or locating a node location, or performing other operations on a node. The process of traversing the binary tree is the process of arranging the nodes of the two-fork tree linearly. Assuming that the operation of the Access node when traversing the binary tree is the value of the output node data field, then the result of the traversal is a linear sequence.
From the recursive definition of the two-fork tree, a non-empty two-fork tree consists of three basic parts, the root node and the left and right subtree. Therefore, on any given node, three operations can be performed in a certain order:
(1) Access node itself (N),
(2) Zuozi (L) traversing the node,
(3) The right sub-tree (R) of the node is traversed.

There are six execution sequences for the above three operations:

　NLR、LNR、LRN、NRL、RNL、RLN。

Attention:
The first three sequences are symmetrical with the last three order, so we only discuss the first three order of left and right.
Since the node visited must be the root of a subtree, n (Node), L (left Subtlee), and R (right subtree) can be interpreted as the tree of the root, the Zoki of the root. NLR, LNR, and LRN are also known as first-root traversal, middle-root traversal, and post-root traversal, respectively.
　　

Pre-order non-recursive

     Public voidPreordernorec (TreeNode root) {//system.out.println ("First order traversal (non-recursive):");        //array simulation stack, assuming that there are no more than 32 nodestreenode[] Stack =Newtreenode[ +]; for(inti =0;i< +; i++) {Stack[i] =NULL; }int Index=0; TreeNode pnode = root; while(pnode!=NULL||Index>0){ while(pnode!=NULL) {System.out.print (Pnode.getkey () +","); stack[Index+ +] = Pnode;            Pnode = Pnode.getleftchlid (); } Pnode = stack[--Index];        Pnode = Pnode.getrightchild (); }//system.out.println ("");}

Recursive

publicvoidpreorder(TreeNode root){        if(root!=null){            System.out.print(root.getKey()+",");            preorder(root.getLeftchlid());            preorder(root.getRightchild());        }    }

Middle order non-recursive

     Public voidInordernorec (TreeNode root) {treenode[] stack =Newtreenode[ +];int Index=0; for(inti =0;i< +; i++) {Stack[i] =NULL; } TreeNode pnode = root; while(pnode!=NULL||Index>0){ while(pnode!=NULL) {stack[Index+ +] = Pnode;            Pnode = Pnode.getleftchlid (); } Pnode = stack[--Index]; System.out.print (Pnode.getkey () +",");        Pnode = Pnode.getrightchild (); }//system.out.println ("");}

Recursive

publicvoidinorder(TreeNode root){        if(root!=null){            inorder(root.getLeftchlid());            System.out.print(root.getKey()+",");            inorder(root.getRightchild());        }    }

Post-Iteration traversal non-recursive

 Public voidPostordernorec (TreeNode root) {treenode[] stack =Newtreenode[ +];int Index=0; for(inti =0;i< +; i++) {Stack[i] =NULL;    } TreeNode pnode = root; TreeNode lastvisit =NULL; while(pnode!=NULL||Index>0){ while(pnode!=NULL) {stack[Index+ +] = Pnode;        Pnode = Pnode.getleftchlid (); } pnode=stack[Index-1];if(Pnode.getrightchild () = =NULL|| Pnode.getrightchild () ==lastvisit) {System.out.print (Pnode.getkey () +","); Lastvisit = Pnode;Index--; Pnode =NULL; }Else{Pnode = Pnode.getrightchild (); }    }}

Recursive

publicvoidpostorder(TreeNode root){    if(root!=null){        postorder(root.getLeftchlid());        postorder(root.getRightchild());        System.out.print(root.getKey()+",");    }}

Reference

http://blog.csdn.net/wuwenxiang91322/article/details/12231657
http://blog.csdn.net/tanyujing/article/details/9381451

Interview Road (one)-java recursive and non-recursive binary tree pre-order traversal