题解 | #判断是不是二叉搜索树#
判断是不是二叉搜索树
https://www.nowcoder.com/practice/a69242b39baf45dea217815c7dedb52b
One-liner 一行代码
public class Solution {
TreeNode pre = null;
public boolean isValidBST (TreeNode root) {
// O(1) space with global pre node
return root == null || isValidBST(root.left) && (pre == null || root.val > pre.val) && ((pre = root) != null) && isValidBST(root.right);
}
}
