98. Validate Binary Search Tree

[Shawngbk]

 递归以后，如果去的是root.left， 之前的节点root.val变成了最大值，同理root.right，root.val变成最小值比较 /**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }
• } */

public class Solution { public boolean isValidBST(TreeNode root) { return helper(root, Long.MIN_VALUE, Long.MAX_VALUE); } private boolean helper(TreeNode root, long minVal, long maxVal) { if(root == null) return true; if(root.val <= minVal || root.val >= maxVal) return false; return helper(root.left, minVal, root.val) && helper(root.right, root.val, maxVal); } }

[Shawngbk]

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