Given the root of a binary tree, find the maximum value V for which there exists 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.)
Example 1:
Input: [8,3,10,1,6,null,14,null,null,4,7,13] Output: 7 Explanation: We have various ancestor-node differences, some of which are given below : |8 - 3| = 5 |3 - 7| = 4 |8 - 1| = 7 |10 - 13| = 3 Among all possible differences, the maximum value of 7 is obtained by |8 - 1| = 7.
因为是比较最大 difference, 可以是正数，也可以是负数。
1 class Solution { 2 public int maxAncestorDiff(TreeNode root) { 3 int[] tempMax = { 0 }; 4 helper(root, root.val, root.val, tempMax); 5 return tempMax[0]; 6 } 7 8 public void helper(TreeNode root, int maxAncestor, int minAncestor, int[] tempMax) { 9 if (root == null) return; 10 tempMax[0] = Math.max(tempMax[0], Math.abs(maxAncestor - root.val)); 11 tempMax[0] = Math.max(tempMax[0], Math.abs(minAncestor - root.val)); 12 maxAncestor = Math.max(maxAncestor, root.val); 13 minAncestor = Math.min(minAncestor, root.val); 14 15 helper(root.left, maxAncestor, minAncestor, tempMax); 16 helper(root.right, maxAncestor, minAncestor, tempMax); 17 } 18 }
1026. Maximum Difference Between Node and Ancestor
原文：https://www.cnblogs.com/beiyeqingteng/p/12636198.html