leetcode1026

public class Solution
    {
        Stack<int> S = new Stack<int>();
        int maxValue = 0;
        public void Trace(TreeNode root)
        {
            if (root != null)
            {
                S.Push(root.val);
                if (root.left != null)
                {
                    Trace(root.left);
                }
                if (root.right != null)
                {
                    Trace(root.right);
                }
                if (root.left == null && root.right == null)
                {

                    var ary = S.ToArray().Reverse().ToList();
                    var len = ary.Count();
                    for (var i = 0; i < len; i++)
                    {
                        for (int j = i + 1; j < len; j++)
                        {
                            maxValue = Math.Max(maxValue, Math.Abs(ary[i] - ary[j]));
                        }
                        //Console.WriteLine(a);
                    }
                    //Console.WriteLine(maxValue);
                }
                S.Pop();
            }
        }
        public int MaxAncestorDiff(TreeNode root)
        {
            Trace(root);
            return maxValue;
        }
    }