Validate Binary Search Tree
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
- The left subtree of a node contains only nodes with keys less than the node's key.
- The right subtree of a node contains only nodes with keys greater than the node's key.
- Both the left and right subtrees must also be binary search trees.
confused what "{1,#,2,3}"
means? > read more on how binary tree is serialized on OJ.
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } * 详细解释 * http://blog.csdn.net/sgbfblog/article/details/7771096 */ public class Solution { public boolean isValidBSTHelper(TreeNode root, int min, int max) { if (root==null) { return true; } return root.val > min && root.val < max && isValidBSTHelper(root.left, min, root.val) && isValidBSTHelper(root.right, root.val, max); } public boolean isValidBST(TreeNode root) { return isValidBSTHelper(root,Integer.MIN_VALUE, Integer.MAX_VALUE); } }