判断一棵树是否是二叉查找树

public boolean isValidBST(TreeNode root) {
return validateRange(root, Long.MIN_VALUE, Long.MAX_VALUE);
}

private boolean validateRange(TreeNode root, long min, long max) {
if (root == null) return true;
if (root.val <=min || root.val >= max)) return false;
return validateRange(root.left, min, (long) root.val)
&& validateRange(root.right, (long) root.val, max);
}

public static boolean judgeBST(TreeNode root,int pre){
if(root==null)return true;
boolean left=judgeBST(root.left,pre);
if(!left)return false;
if(root.val<=pre)return false;
pre=root.val;
boolean right=judgeBST(root.right,pre);
if(!right)return false;
return true;
}