leetcode_230题——Kth Smallest Element in a BST（二叉搜索树，中序遍历）

Kth Smallest Element in a BST

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Question  Solution 

 

Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.

Note: 
You may assume k is always valid, 1 ≤ k ≤ BST's total elements.

Follow up:
What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?

Show Hint 

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

 

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  (M) Binary Tree Inorder Traversal

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      这道题采用中序遍历的方法，在遍历时记录下遍历的第几个就可以了

#include<iostream>
using namespace std;
struct TreeNode {
      int val;
      TreeNode *left;
      TreeNode *right;
      TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 };
int num=0;//记录次数
int re;//记录最终结果

//中序遍历的方法
void digui(TreeNode* root, int k)
{
    if(root->left!=NULL)
        digui(root->left,k);
    num++;
    if(num==k)
        re=root->val;
    if(root->right!=NULL)
        digui(root->right,k);
    return;
}

int kthSmallest(TreeNode* root, int k) {
    digui(root,k);
    return re;
}
int main()
{

}