98. Validate Binary Search Tree

注意转换类型 别忘了加long 

 

 

class Solution {
    public boolean isValidBST(TreeNode root) {
        return helper(root, (long)Integer.MAX_VALUE + 1, (long)Integer.MIN_VALUE - 1); //万一有node就是maxvalue 所以要+1 min同理
        
    }
    
    public boolean helper(TreeNode root, long max, long min) {
        if(root == null) return true;
        return ((root.val > min) && (root.val < max) && (helper(root.left, Math.min(max, root.val), min)) && (helper(root.right, max, Math.max(min, root.val))));
    }
}