题解 | #二叉搜索树的第k个结点#

中序遍历解决问题

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

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

    }

}
*/
import java.util.ArrayList;
public class Solution {
    ArrayList<TreeNode> save = new ArrayList<>();
    TreeNode KthNode(TreeNode pRoot, int k) {
        if(pRoot == null){
            return null;
        }
        inorder(pRoot);
        if(k <= 0 || k > save.size()){
            return null;
        }
        return save.get(k-1);
    }
    public ArrayList<TreeNode> inorder(TreeNode root){
        if(root == null){
            return null;
        }
        if(root.left != null){
            inorder(root.left);
        }
        save.add(root);
        if(root.right != null){
            inorder(root.right);
        }
        return save;
    }

}