leetcode(98)：判断是否为搜索二叉树

题目

98. 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.
Example 1:

Input:
2
/
1 3
Output: true
Example 2:

5

/
1 4
/
3 6
Output: false
Explanation: The input is: [5,1,4,null,null,3,6]. The root node’s value
is 5 but its right child’s value is 4.

递归解法

class Solution {
public:


	void getResult(TreeNode* root, bool &result, long &minnum,long &maxnum) {
		if (root == nullptr)
			return;
		getResult(root->left, result,minnum, maxnum);
		if (root->val <=minnum) {
			result = false;
		}
		minnum = root->val;
		getResult(root->right, result, minnum,maxnum);
	}

	bool isValidBST(TreeNode* root) {
		long minnum = INT64_MIN;              //防止最初节点为INT_MIN
		long maxnum = INT64_MAX;
		if (root == nullptr)
			return true;
		bool result = true;
		getResult(root, result, minnum,maxnum);
		return result;
	}
};