Algorithm 4 Binary Tree Traversal Nonrecursive

Require: a binary tree $T$

Ensure: print all keys appearing in $T$

1:Let $S$ be a stack

2:Push( $S, T.root$ )

3:while not StackEmpty( $S$ ) do

4: $x =$ Pop( $S$ )

5:if $x == NIL$ then

6:continue

7:end if

8:print $x.key$

9:Push( $x.right$ )

10:Push( $x.left$ )

11:end while