230. 二叉搜索树中第K小的元素二叉搜索数

Posted 2021-11-04 幽殇默

https://leetcode-cn.com/problems/kth-smallest-element-in-a-bst/

/**
 * 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>ans;
    int kthSmallest(TreeNode* root, int k) 
    {
        dfs(root,k);
        return ans[k-1];
    }
    void dfs(TreeNode* root,int k)
    {
        if(!root) return;
        if(ans.size()>=k) return;
        if(root->left)  dfs(root->left,k);
        ans.push_back(root->val);
        if(root->right) dfs(root->right,k);
    }
};