[LeetCode] Validate Binary Search Tree

hale1007

于 2014-10-29 22:14:59 发布

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分类专栏： LeetCode Algorithm

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本文介绍了一种检查给定二叉树是否为有效二叉搜索树的方法。通过递归方式验证每个节点的值是否在其合法范围内，并确保左右子树也符合二叉搜索树的定义。

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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.

/**
 * 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 check(root, INT_MIN, INT_MAX);
    }
    bool check(TreeNode *root, int left, int right)
    {
        if(root == nullptr) return true;
        return left < root->val && right > root->val && check(root->left, left, root->val) && check(root->right, root->val, right);
    }
};

参考：http://www.cnblogs.com/remlostime/archive/2012/11/16/2772629.html