230.kth-smallest-element-in-a-bst.cpp

/*
 * @lc app=leetcode id=230 lang=cpp
 *
 * [230] Kth Smallest Element in a BST
 */

// @lc code=start
/**
 * 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> vtr;
    int kthSmallest(TreeNode *root, int k)
    {
        enter(root);
        return vtr[k-1];
    }
    void enter(TreeNode *n)
    {
        if (!n)
            return;
        enter(n->left);
        vtr.push_back(n->val);
        enter(n->right);
    }
};
// @lc code=end