题解 | #二叉搜索树的第k个节点#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param proot TreeNode类 
     * @param k int整型 
     * @return int整型
     */
    private List<Integer> nodeList = new ArrayList<>();
    public int KthNode (TreeNode proot, int k) {
        // write code here
        if(proot == null) return -1;
        if(k==0) return -1;
        dfs(proot, k);
        if(k <= nodeList.size()){
            return nodeList.get(k-1);
        }
        return -1;
    }

    public void dfs(TreeNode tree, int k){
        if(tree == null) return;
        dfs(tree.left, k);
        nodeList.add(tree.val);
        if(nodeList.size() == k) return;
        dfs(tree.right,k);
    }
}