98. Validate Binary Search Tree

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public boolean isValidBST(TreeNode root) {
12         return root == null ? true : isValidBST(root.left, Integer.MIN_VALUE, root.val, true, false) 
　　　　　　　　&& isValidBST(root.right, root.val, Integer.MAX_VALUE, false, true);
13     }
14     public boolean isValidBST(TreeNode root, int smallVal, int largeVal, boolean isLeft, boolean isRight){
15         if(root == null)
16             return true;
17         else if((!isRight && root.val >= largeVal) || (!isLeft && root.val <= smallVal))
18             return false;
19         else
20             return isValidBST(root.left, smallVal, root.val, isLeft, false) && 
　　　　　　　　　　isValidBST(root.right, root.val, largeVal, false, isRight);
21     }
22     
23 }