Valid Binary Search Tree

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { public boolean isValidBST(TreeNode root) { return isValid(root,-1001,1001); } // inorder dfs public boolean isValid(TreeNode root,int l, int r){ if(root ==null) return true; boolean left = isValid(root.left,l,root.val); //root.val should always be greater than its left child value and less that its right chil value if(root.val <=l || root.val>=r) return false; boolean right = isValid(root.right,root.val, r); return left && right; } }