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