LeetCode [1026] Maximum Difference Between Node and Ancestor

 1026. Maximum Difference Between Node and Ancestor

Medium

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.

 

Note:

1. The number of nodes in the tree is between 2 and 5000.
2. Each node will have value between 0 and 100000.

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/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { int dm = 0; public int maxAncestorDiff(TreeNode root) { if(root==null) return dm; helper(root, root.val, root.val); return dm; } void helper(TreeNode root, int aMax, int aMin){ if(root==null) return; int d = Math.max(Math.abs(root.val-aMax), Math.abs(root.val-aMin)); dm = Math.max(dm, d); aMax = Math.max(aMax, root.val); aMin = Math.min(aMin, root.val); helper(root.left, aMax, aMin); helper(root.right, aMax, aMin); } }