Validate Binary Search Tree

ststns

于 2015-04-15 14:37:01 发布

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分类专栏：学习文章标签： leetcode

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本文介绍如何通过递归方法验证给定的二叉树是否为有效的二叉搜索树，详细解释了BST的性质，并提供了实现代码。

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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.

Just the property of bst, trick with long_min and max

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isValidBST(TreeNode *root) {
        return helper(root, LONG_MIN,LONG_MAX);
    }
    
    bool helper(TreeNode* root, long min, long max){
        if (root==0)
            return true;
        if (root->val<=min || root->val>=max)
            return false;
        return helper(root->left, min,root->val ) && helper(root->right, root->val, max);
    }
};