LeetCode:Validate Binary Search Tree

Validate Binary Search Tree

Total Accepted: 96991 Total Submissions: 459613 Difficulty: Medium

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.

Example 1:

    2   / \  1   3

Binary tree [2,1,3], return true.

Example 2:

    1   / \  2   3

Binary tree [1,2,3], return false.

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java code:

/** * 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) {        long minVal = Long.MIN_VALUE;        long maxVal = Long.MAX_VALUE;        return isValidBST(root, minVal, maxVal);    }        // 自定义函数    private boolean isValidBST(TreeNode root, long minVal, long maxVal) {                if(root == null) return true;        if(root.val <= minVal || maxVal <= root.val) return false;                return isValidBST(root.left, minVal, root.val) && isValidBST(root.right, root.val, maxVal);    }}