In Order Successor in Binary Search Tree

Question

Given a node in a BST, how does one find the next higher key?

Answer 1

These answers all seem overly complicated to me. We really don't need parent pointers or any auxiliary data structures like a stack. All we need to do is traverse the tree from the root in-order, set a flag as soon as we find the target node, and the next node in the tree that we visit will be the in order successor node. Here is a quick and dirty routine I wrote up.

Node* FindNextInorderSuccessor(Node* root, int target, bool& done)
{
    if (!root)
        return NULL;

    // go left
    Node* result = FindNextInorderSuccessor(root->left, target, done);
    if (result)
        return result;

    // visit
    if (done)
    {
        // flag is set, this must be our in-order successor node
        return root;
    }
    else
    {
        if (root->value == target)
        {
            // found target node, set flag so that we stop at next node
            done = true;
        }
    }

    // go right
    return FindNextInorderSuccessor(root->right, target, done);
}