Binary Tree Traversal (Reverse Preorder)

Question

I want to have a vector that pushes in 'R' everytime the tree traverses to the right subtree and pushes in 'L' everytime the tree traverse to a left subtree.

void reverse_preorder(BTree<string>* root)
{ vector<string>a;
    if (root != NULL) {
        a.push_back("R");
        if(root->right == NULL) a.push_back("L");
        reverse_preorder(root->right);
        reverse_preorder(root->left);
    }
}

but for some reason the output im getting is not in the correct order. What am I doing wrong?

Answer 1

Make the vector a member of your class. Then

void reverse_preorder(BTree<string>* root)
{
    if (root != NULL) {
        if (root->right != NULL) a.push_back("R");
        reverse_preorder(root->right);
        if (root->left != NULL) a.push_back("L");
        reverse_preorder(root->left);
    }
}

Though, I don't see how it will help you to do a 'pretty' formatting.