maximum-difference-between-node-and-ancestor¶

Description¶

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.

Example 1:

Input: root = [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.

Example 2:

Input: root = [1,null,2,null,0,3]
Output: 3

Constraints:

The number of nodes in the tree is in the range [2, 5000].
0 <= Node.val <= 10⁵

Solution(Python)¶

class Solution:
    def maxAncestorDiff(self, root, curMin=inf, curMax=-inf):
        if not root:
            return curMax - curMin

        if root.val < curMin:
            curMin = root.val

        if root.val > curMax:
            curMax = root.val

        left = self.maxAncestorDiff(root.left, curMin, curMax)
        right = self.maxAncestorDiff(root.right, curMin, curMax)

        if left > right:
            return left
        else:
            return right