leetcode[98]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

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

/*

类型名称             字节数         取值范围

signed char            1           -128～+127

short int              2           -32768～+32767

int                    4        -2147438648～+2147438647

long int               4        -2147438648～+2141438647

long long int          8     -9223372036854775808～+9223372036854775807

*/

bool check(TreeNode *node, long long leftmin, long long rightmax)

{

    if(node==NULL)return true;

    return (node->val>leftmin&&node->val<rightmax)&&check(node->left,leftmin,node->val)&&check(node->right,node->val,rightmax);

}

    bool isValidBST(TreeNode *root) {

        return check(root,-9223372036854775808,9223372036854775807);

    }

};