LeetCode 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:
2
/ \
1 3
Binary tree [2,1,3], return true.
Example 2:
1
/ \
2 3
Binary tree [1,2,3], return false.

题目大意:给一个二叉树,判断这个二叉树是不是合法的二叉搜索树~

分析:既然是二叉搜索树,那么按照左根右遍历后的结果一定是增序~所以只需要中序遍历一遍,判断遍历结果的数组是不是后面数一定大于前面数就可以了~