Predecessor_and_Successor_in_BST.cpp

void solve(BinaryTreeNode<int> *root, int key, int &pre, int &suc)
{
    if (root == nullptr)
    {
        return;
    }
    solve(root->left, key, pre, suc);
    if (root->data < key)
    {
        pre = root->data;
    }
    if (root->data > key and suc == -1)
    {
        suc = root->data;
    }
    solve(root->right, key, pre, suc);
}
pair<int, int> predecessorSuccessor(BinaryTreeNode<int> *root, int key)
{
    // Write your code here.
    int pre = -1;
    int suc = -1;
    if (root == nullptr)
    {
        return {-1, -1};
    }
    solve(root, key, pre, suc);
    return {pre, suc};
}