题目描述
给定一棵二叉查找树，实现一个实现查询树中第k小的方法kthSmallest。

注意
假设 k 总是合法，即1 ≤ k ≤ BST的总元素个数。
样例
Example 1:

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

2
Output: 1

Example 2:

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

思路

中序遍历就是有序的，利用二叉搜索这个性质

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int kthSmallest(TreeNode* root, int k) {
        vector<TreeNode*> nodeList;
        dfs(root,nodeList);
        return nodeList[k-1]->val;
    }
    void dfs(TreeNode* cur,vector<TreeNode*>& nodeList){
        if(cur->left) dfs(cur->left,nodeList);
        nodeList.push_back(cur);
        if(cur->right) dfs(cur->right,nodeList);
    }
   
};

标签：right,TreeNode,cur,int,大值,50,dfs,二叉树,nodeList
来源： https://blog.csdn.net/qq_34673038/article/details/90205985