2026/04/05

[LeetCode] 230 Kth Smallest Element in a BST

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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:
  void inOrderTraverse(TreeNode* node, std::vector<int>& v) {
    if (node == nullptr)
      return;
    inOrderTraverse(node->left, v);
    v.push_back(node->val);
    inOrderTraverse(node->right, v);
  }

  int kthSmallest(TreeNode* root, int k) {
    std::vector<int> v;
    inOrderTraverse(root, v);
    return v[k - 1];
  }
};