Recursive non-recursive recursion of binary tree traversal

Recursive

//Recursive first-order traversal     Public Static voidPre (TreeNode root) {if(root==NULL)return;        Visit (Root); if(root.left!=NULL) Pre (root.left); if(root.right!=NULL) Pre (root.right); }         //Recursive middle order traversal     Public Static voidIn (TreeNode root) {if(Root = =NULL)return; if(root.left!=NULL) in (Root.left);          Visit (Root); if(root.right!=NULL) in (root.right); }          //recursive post-sequential traversal     Public Static voidpost (TreeNode root) {if(Root = =NULL)return; if(root.left!=NULL) in (Root.left); if(root.right!=NULL) in (root.right);         Visit (Root); }

Non-recursive:

//non-recursive pre-sequence traversal--Stack     Public Static voidpretraverse (TreeNode root) {Stack<TreeNode> s=NewStack<treenode>();        S.push (root);  while(!S.isempty ()) {TreeNode current=S.pop ();            Visit (current); if(current.right!=NULL) S.push (current.right); if(current.left!=NULL) S.push (current.left); }            }    //non-recursive pre-sequence traversal--queue     Public Static voidpreTraverse2 (TreeNode root) {Queue<TreeNode> q=NewLinkedlist<treenode>();        Q.offer (root);  while(!Q.isempty ()) {TreeNode current=Q.poll ();            Visit (current); if(current.left!=NULL) Q.offer (current.left); if(current.right!=NULL) Q.offer (current.right); }            }    //non-recursive mid-order traversal     Public Static voidintraverse (TreeNode root) {Stack<TreeNode> s=NewStack<treenode>(); TreeNode T=Root;  while(!s.isempty () | | t!=NULL){            if(t!=NULL) {s.push (t); T=T.left; }Else{T=S.pop ();                Visit (t); T=T.right; }        }            }

Recursive non-recursive recursion of binary tree traversal