Question: WAP to find Kth minimum element in a Binary Searth Tree.


Count number of nodes in the tree if they are less then k return.
If (no_of_nodes(node->left) == k-1) return node->data
If (no_of_nodes(node->left) >= k) findkthmin(node->left,k)
else findkthmin(node->right, (k - no_of_nodes(node->left) -1))



struct treenode{
int data;
struct treenode * left;
struct treenode * right;

int no_of_nodes(struct treenode * node)
if(node == NULL)
return 0;
return(1 + no_of_nodes(node->left) + no_of_nodes(node->right));

int findkthmin(struct treenode * node, int k)
int no_nodes = no_of_nodes(node->left);
if (no_nodes == k-1)
return node->data;
if (no_nodes >= k)
return findkthmin(node->left,k);
return findkthmin(node->right, (k - no_nodes - 1));

void main()
struct treenode * tree;
int k, min;
tree = createtree(); /*create a BST*/
if (no_of_nodes(tree) < k)
printf("Number of nodes in tree are less than %d \n",k);
min = findkthmin(tree, k);
printf("kth min element = %d\n",min);

This solution can be optimized by saving the no of nodes in each subtree while calling no_of_nodes(tree) for root.

For finding kth maximum element, similar logic can be used.

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