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.
confused what "{1,#,2,3}"
means? > read more on how binary tree is serialized on OJ.
1 /** 2 * Definition for binary tree 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 checkBST(root,Long.MIN_VALUE,Long.MAX_VALUE); 13 } 14 15 private boolean checkBST(TreeNode node,long leftval,long rightval){ 16 if (node==null) return true; 17 return leftval<node.val && node.val<rightval && checkBST(node.left,leftval,node.val) 18 && checkBST(node.right,node.val,rightval); 19 20 } 21 }