# Kth Smallest Element In A BST Problem

## Description

LeetCode Problem 230.

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

Example 1:

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

Example 2:

``````1
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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 <= 10^4
• 0 <= Node.val <= 10^4

## Sample C++ Code

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/**
* 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:
vector<int> sorted;
void inorder(TreeNode* node) {
if (node == NULL)
return;
inorder(node->left);
sorted.push_back(node->val);
inorder(node->right);
}

int kthSmallest(TreeNode* root, int k) {
inorder(root);
return sorted[k-1];
}
};
``````