问题
Can anyone give me a solution for traversing a binary tree in inorder without recursion and without using a stack?
回答1:
Second edit: I think this is right. Requires node.isRoot, node.isLeftChild, and node.parent, in addition to the usual node.left_child and node.right_child.
state = "from_parent"
current_node = root
while (!done)
switch (state)
case "from_parent":
if current_node.left_child.exists
current_node = current_node.left_child
state = "from_parent"
else
state = "return_from_left_child"
case "return_from_left_child"
if current_node.right_child.exists
current_node = current_node.right_child
state = "from_parent"
else
state = "return_from_right_child"
case "return_from_right_child"
if current_node.isRoot
done = true
else
if current_node.isLeftChild
state = "return_from_left_child"
else
state = "return_from_right_child"
current_node = current_node.parent
回答2:
Since traversing a binary tree requires some kind of state (nodes to return after visiting successors) which could be provided by stack implied by recursion (or explicit by an array).
The answer is no, you can't. (according to the classic definition)
The closest thing to a binary tree traversal in an iterative way is probably using a heap
EDIT: Or as already shown a threaded binary tree ,
回答3:
Yes, you can. In order to do this, you would require a parent pointer in order to ascend the tree.
回答4:
Start with tree_first(), continue with tree_next() until get NULL. Full code: https://github.com/virtan/tree_closest
struct node {
int value;
node *left;
node *right;
node *parent;
};
node *tree_first(node *root) {
while(root && root->left)
root = root->left;
return root;
}
node *tree_next(node *p) {
if(p->right)
return tree_first(p->right);
while(p->parent) {
if(!p->parent->right || p->parent->right != p)
return p->parent;
else p = p->parent;
}
return 0;
}
回答5:
As someone here already stated, it is possible, but not without the parent pointer. The parent pointer basically allows you to traverse "the path" if you want, and therefore print-out the nodes. But why does recursion works without parent pointer? Well if you understand recursion it goes something like this(imagine the recursion stack):
recursion //going into
recursion
recursion
recursion
recursion //going back up
recursion
recursion
recursion
So when the recursion ends you then have printed the chosen side of the binary tree in reversed order.
来源:https://stackoverflow.com/questions/2595002/can-i-do-inorder-traversal-of-a-binary-tree-without-recursion-and-stack