Leetcode 230. Binary search tree small element K (balance tree)

Topic

Given a binary search tree, write a function kthsmallest to find the k smallest element.

Description
You can assume that K is always valid, 1≤k≤ two forks to search for the number of tree elements.

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
Advanced:
If the binary search tree is often modified (insert/delete operations) and you need to find k the small value frequently, how would you optimize the kthSmallest function?

Exercises

Writing leetcode for the first time is not very good.

In the public definition of a function recursive sequence traversal, record the answer, found when return it can.

Do not spit slot variable name

/** * 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 index = 0, final_attack_ride;  void Solve(TreeNode* root, const int &k) {    if (root->left) {      Solve(root->left, k);    }    if (index >= k) return;    if (++index == k) {      final_attack_ride = root->val;      return;    }    if (root->right) {      Solve(root->right, k);    }  }  int kthSmallest(TreeNode* root, int k) {    Solve(root, k);    return final_attack_ride;  }};

Leetcode 230. Binary search tree small element K (balance tree)