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);

    }

};

巴特西

LC 98. Validate Binary Search Tree

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