230. Kth Smallest Element in a BST | LeetCode Solution

 230. Kth Smallest Element in a BST

Given the root of a binary search tree, and an integer k, return the kth smallest value (1-indexed) of all the values of the nodes in the tree.

 

Example 1:

Input: root = [3,1,4,null,2], k = 1
Output: 1

Example 2:

Input: root = [5,3,6,2,4,null,null,1], k = 3
Output: 3

 

Constraints:

• The number of nodes in the tree is n.
• 1 <= k <= n <= 104
• 0 <= Node.val <= 104

The solution to the above question is-

/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}

 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}

 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}

 * };

 */

class Solution {

public:

    int n=0;

    int ans=0;

    void inorder(TreeNode* root,int k){

        if(root==NULL)return;

        

        inorder(root->left,k);

        n++;

        if(n==k)ans=root->val;

        inorder(root->right,k);

    }

    

    

    int kthSmallest(TreeNode* root, int k) {

        

        inorder(root,k);

        return ans;

    }

};