代码随想录——验证二叉搜索树（Leetcode98）

题目链接

递归

一个有效的二叉搜索树中序遍历应该是一个递增序列

/*** 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 {ArrayList<Integer> array = new ArrayList<>();public boolean isValidBST(TreeNode root) {inOrder(root);for(int i = 1; i < array.size(); i++){if(array.get(i) <= array.get(i - 1)){return false;}}return true;}// 中序遍历public void inOrder(TreeNode root){if(root == null){return ;}inOrder(root.left);array.add(root.val);inOrder(root.right);}
}