# Java Big Numbers

draft-post/2019-12-27 Fang

## Example 1

Validate a BST Given a binary tree, determine if it is a valid binary search tree (BST).

Buggy code:

``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isValidBST(TreeNode root) {
if(root == null)
return true;
return checkNode(root.left, Integer.MIN_VALUE, root.val) && checkNode(root.right, root.val, Integer.MAX_VALUE);
}

public boolean checkNode(TreeNode n, int floor, int ceil){
if(n == null)
return true;
if(n.val <= floor || n.val >= ceil)
return false;
return checkNode(n.left, floor, n.val) && checkNode(n.right, n.val, ceil);
}
}``````

### Corner Cases

[-2147483648,null,2147483647] [2147483647,null,2147483647]

Fix problem just by switching to a bigger container:

``````class Solution {
public boolean isValidBST(TreeNode root) {
if(root == null)
return true;
return checkNode(root.left, Long.MIN_VALUE, root.val) && checkNode(root.right, root.val, Long.MAX_VALUE);
}

public boolean checkNode(TreeNode n, long floor, long ceil){
if(n == null)
return true;
if(n.val <= floor || n.val >= ceil)
return false;
return checkNode(n.left, floor, n.val) && checkNode(n.right, n.val, ceil);
}
}``````