Question

write the method that return the kth smallest item in the binary search tree. for example if the tree has 18 node and the user enter 13 then the method should return the 13 smallest element in the tree. I has a method that done it recursively but I want to Implement findKth nonrecursively

public String findKth( String k )
{ return findKth( k, root).data; }
public Node findKth(int k, Node t ) {
  
     
   if( t == null )
   throw new IllegalArgumentException( );
   int leftSize = ( t.left != null ) ? ( t.left).size() : 0;

   if( k <= leftSize )
   return findKth( k, t );
   if( k == leftSize + 1 )
   return t;
   return findKth( k - leftSize - 1, t.right );
   }

I appreciate any help :)

Answer 1

Answer:

We can inorder traverse the tree and get the kth smallest element in O(n) time.

public int findKth(Node root, int k) {
    Stack<Node> stack = new Stack<Node>();
 
    Node p = root;
    int result = 0;
 
    while(!stack.isEmpty() || p!=null){
        if(p!=null){
            stack.push(p);
            p = p.left;
        }else{
            Node t = stack.pop();
            k--;
            if(k==0)
                result = t.val;
            p = t.right;
        }
    }
 
    return result;
}

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