leetcode1026

 public class Solution
     {
         Stack<int> S = new Stack<int>();
         int maxValue = ;
         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 = ; i < len; i++)
                     {
                         for (int j = i + ; 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;
         }
     }