Several Traversal Algorithms of the c ++ Binary Tree

1. pre-order/middle-order/post-order traversal (Recursive Implementation)

Copy codeThe Code is as follows: // pre-order traversal
Void BT_PreOrder (BiTreePtr pNode ){
If (! PNode) return;
Visit (pNode );
BT_PreOrder (pNode-> left );
BT_PreOrder (pNode-> right );}
// Sequential Traversal
Void BT_PreOrder (BiTreePtr pNode ){
If (! PNode) return;
BT_PreOrder (pNode-> left );
Visit (pNode );
BT_PreOrder (pNode-> right );}
// Post-order traversal void BT_PreOrder (BiTreePtr pNode ){
If (! PNode) return;
BT_PreOrder (pNode-> left );
BT_PreOrder (pNode-> right );
Visit (pNode );}

2. pre-order traversal (non-Recursive Implementation)Copy codeThe Code is as follows: // stack implementation
Void BT_PreOrderNoRec1 (BiTreePtr pNode ){
Stack <BiTreePtr> s;
While (! PNode |! S. empty ())
{
If (! PNode)
{
Visit (pNode );
S. push (pNode );
PNode = pNode-> left;
}
Else
{
PNode = s. pop ();
PNode = pNode-> right;
}
}
}
// Stack implementation
Void BT_PreOrderNoRec2 (BiTreePtr pNode ){
If (! PNode)
{
Stack <BiTreePtr> s;
S. push (pNode );
While (! S. empty ())
{
BiTreePtr pvNode = s. pop ();
Visit (pvNode );
S. push (pvNode-> right );
S. push (pvNode-> left );
}
}}
//
No stack is required. Each node contains the parent node pointer and isVisited [false by default] status variable, and the binary tree contains a header node.
Void BT_PreOrderNoRec3 (BiTreePtr pNode ){
While (! PNode)
// Go back To the header node pointing to the root node and exit.
{
If (! PNode-> bVisited)
// Determine whether the object has been accessed
{
Visit (pNode );
PNode-> isVisited = true;
}
If (pNode-> left &&! PNode-> left-> isVisited)
PNode = pNode-> left;
Else if (pNode-> right &&! PNode-> right-> isVisited)
PNode = pNode-> right;
Else
// Backtracking
PNode = pNode-> parent;
}}

3. Sequential traversal (non-Recursive Implementation)

Copy codeThe Code is as follows: // stack implementation
Void BT_InOrderNoRec1 (BiTreePtr pNode ){
Stack <BiTreePtr> s;
While (! PNode |! S. empty ())
{
If (! PNode)
{
S. push (pNode );
PNode = pNode-> left;
}
Else
{
PNode = s. pop ();
Visit (pNode );
PNode = pNode-> right;
}
}}
// No stack is required. Each node includes the parent node pointer and isVisited [false by default] status variable, and the binary tree contains a header node.
Void BT_InOrderNoRec2 (BiTreePtr pNode ){
While (! PNode)
// Go back To the header node pointing to the root node and exit.
{
While (pNode-> left &&! PNode-> left-> isVisited)
PNode = pNode-> left;
If (! PNode-> isVisited)
{
Visit (pNode );
PNode-> isVisited = true;
}
If (pNode-> right &&! PNode-> right-> isVisited)
PNode = pNode-> right;
Else
PNode = pNode-> parent;
}}

4. Post-order traversal (non-Recursive Implementation)Copy codeCode: void BT_PostOrderNoRec (BiTreePtr pNode ){
If (! PNode) return;
Stack <BiTreePtr> s;
S. push (pNode );
While (! S. empty ())
{
BiTreePtr pvNode = s. pop ();
If (pvNode-> isPushed)
// Indicates that both left and right sub-trees have been written into the stack to access the node
Visit (pvNode );
Else
{
If (pvNode-> right)
{
PvNode-> right-> isPushed = false;
S. push (pvNode-> right );
}
If (pvNode-> left)
{
PvNode-> left-> isPushed = false;
S. push (pvNode-> left );
}
PvNode-> isPushed = true;
S. push (pvNode );
}
}}

5. Sequence traversal (using queues)

Copy codeCode: void BT_LevelOrder (BiTreePtr pNode ){
If (! PNode) return;
Queue <BiTreePtr> q;
Q. push (pNode );
BiTreePtr pvNode;
While (! Q. empty ())
{
PvNode = q. pop ();
Visit (pvNode );
If (pvNode-> left)
Q. push (pvNode-> left );
If (pvNode-> right)
Q. push (pvNode-> right );
}}