Given the root of a binary tree, find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b.
A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor of b.
\n
Example 1:
\n![\"\"](\"https://assets.leetcode.com/uploads/2020/11/09/tmp-tree.jpg\")
\n\nInput: root = [8,3,10,1,6,null,14,null,null,4,7,13]\nOutput: 7\nExplanation: We have various ancestor-node differences, some of which are given below :\n|8 - 3| = 5\n|3 - 7| = 4\n|8 - 1| = 7\n|10 - 13| = 3\nAmong all possible differences, the maximum value of 7 is obtained by |8 - 1| = 7.\n\n
Example 2:
\n![\"\"](\"https://assets.leetcode.com/uploads/2020/11/09/tmp-tree-1.jpg\")
\n\nInput: root = [1,null,2,null,0,3]\nOutput: 3\n\n\n
\n
Constraints:
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