【leetcode hot 100 230】二叉搜索树中第K小的元素
解法一：从小到大输出到list中，取list[k-1]就是第k小的元素
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
List<Integer> list = new ArrayList<>();
public int kthSmallest(TreeNode root, int k) {
// 从小到大输出到list中，取list[k-1]就是第k小的元素
inoder(root);
return list.get(k-1);
}
public void inoder(TreeNode root){
if(root==null){
return;
}
inoder(root.left);
list.add(root.val);
inoder(root.right);
}
}
注意：
list[k-1]是第k小的元素，而不是list[k]