## Title description

Given a binary search tree, please find the k-th smallest node in it. For example, in (5,3,7,2,4,6,8), the value of the third small node is 4 in the order of node value.

## Idea analysis

The characteristics of the binary search tree are: the left node is larger than the root node, and the right node is smaller than the root node.
The result of the middle order traversal is: left-"middle-" right
The combination of the two is an ordered sequence.

## Code

``````import java.util.ArrayList;
/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
this.val = val;

}

}
*/
public class Solution {

ArrayList<TreeNode> list = new ArrayList<>();
TreeNode KthNode(TreeNode pRoot, int k)
{

KthHelper(pRoot);
if(k>=1&&k<=list.size()){

return list.get(k-1);
}
return null;
}
//使用中序遍历：左 中 右
void KthHelper(TreeNode root){

if(root!=null){

KthHelper(root.left);
KthHelper(root.right);
}
}

}
``````

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Origin blog.csdn.net/H1517043456/article/details/107593418
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