98. 验证二叉搜索树

深度搜索优先

/** * 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 { public boolean isValidBST(TreeNode root) { return dfs(root, Long.MIN_VALUE, Long.MAX_VALUE); } public boolean dfs(TreeNode root, long min, long max) { if (root == null) return true; //超出边界 if (root.val <= min || root.val >= max) { return false; } return dfs(root.left, min, root.val) && dfs(root.right, root.val, max); } }