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.
OJ's Binary Tree Serialization:
The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.
Here's an example:
1 / \ 2 3 / 4 \ 5The above binary tree is serialized as
"{1,2,3,#,#,4,#,#,5}"
.用两个值分别作max和min不是一个好办法。
/** * 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) { if(root == NULL)return 1; return isBST(root->left,-1000000,root->val) && isBST(root->right,root->val,1000000); } bool isBST(TreeNode *root, int min ,int max ) { if(root == NULL)return 1; if(root->val >=max || root->val <= min)return 0; return isBST(root->left,min,root->val) && isBST(root->right,root->val,max); } };
posted on 2014-03-17 22:20 pengyu2003 阅读(117) 评论(0) 编辑 收藏 举报