LC 98. Validate Binary Search Tree
题目描述
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.
Example 1:
2 / \ 1 3 Input: [2,1,3] Output: true
Example 2:
5 / \ 1 4 / \ 3 6 Input: [5,1,4,null,null,3,6] Output: false Explanation: The root node's value is 5 but its right child's value is 4.
参考答案
class Solution { public: bool isValidBST(TreeNode* root) { return foo(root,NULL,NULL); } bool foo(TreeNode* root,TreeNode* minNode,TreeNode* maxNode){ if(!root) return true; if(minNode && root->val <= minNode->val || maxNode && root->val >= maxNode->val) return false; return foo(root->left,minNode,root) && foo(root->right,root,maxNode); } };
答案分析