leetcode 230. 二叉搜索树中第K小的元素

/**
 * 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> vec;
    vector<int> t(TreeNode* root)
    {
        if(root)
        {
            vec.push_back(root->val);
            t(root->left);
            t(root->right);
        }
        return vec;
    }
    int kthSmallest(TreeNode* root, int k) {
        t(root);
        //vector<int> temp = t(root);
        //sort(temp.begin(), temp.end());
        sort(vec.begin(), vec.end());
        return vec[k - 1];
    }
};