https://www.geeksforgeeks.org/batch/gfg-160-problems/track/tree-gfg-160/problem/find-k-th-smallest-element-in-bst

class Solution {
  public:
    // Return the Kth smallest element in the given BST
    int kthSmallest(Node *root, int k) {
        // add code here.
        int count =0 ;
        
        int res = -1;
        
        
        helper(root , k , count , res);
        return res;
    }
    
  private:
    void helper(Node *root, int k , int & count , int & res){
        if(!root) return;
        
        helper(root->left , k , count ,  res);
        
        count++;
        
        if(count == k) {
            res = root->data;
            return;
        }
        
        helper(root->right , k , count , res);
        
    }
};

⚙️ Time and Space Complexity

• Time Complexity:
  • Average case: O(H + k) where H is the height of the tree.
  • Worst case (unbalanced tree): O(n)
• Space Complexity: O(H) for the recursive stack (H = height of tree)