Validate Binary Search Tree
给一个二叉树, 问是不是bst. 就利用bst的性质验证.
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/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { double lastval = Long.MIN_VALUE; public boolean isValidBST(TreeNode root) { if(root == null) return true; if(!isValidBST(root.left)) return false; if(lastval>=root.val) return false; lastval = root.val; if(!isValidBST(root.right)) return false; return true; } } |