【hot100-java】二叉搜索树中第 K 小的元素

二叉树

二叉搜索树的中序遍历是递增序列。

/*** 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 {int ret,k;void dfs(TreeNode root){if(root==null) return;dfs(root.left);if(k==0) return;if(--k==0) ret=root.val;dfs(root.right);}public int kthSmallest(TreeNode root, int k) {this.k=k;dfs(root);return ret;}
}