思路:定义一个全局变量,初值赋予k.中序遍历,每次访问一个,变量–,当该变量为0时,就把val值赋予另一个全局变量返回.
class Solution {int resKthSmallest=0;int countKthSmallest;// 276 t230 二叉搜索树第k小的元素public int kthSmallest(TreeNode root, int k) {countKthSmallest=k;kthSmallestDG(root);return resKthSmallest;}public void kthSmallestDG(TreeNode root) {if (root==null){return;}kthSmallestDG(root.left);countKthSmallest--;if (countKthSmallest==0){resKthSmallest=root.val;return;}kthSmallestDG(root.right);}
}