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); } };