#include <limits>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
    int maxAncestorDiff(TreeNode *node, int lower, int upper) const {
        if (node == nullptr) {
            return 0;
        }

        auto diff =
            std::max(std::abs(node->val - lower), std::abs(node->val - upper));
        auto [next_lower, next_upper] = std::make_tuple(
            std::min(lower, node->val), std::max(upper, node->val));

        diff =
            std::max(diff, maxAncestorDiff(node->left, next_lower, next_upper));
        diff = std::max(diff,
                        maxAncestorDiff(node->right, next_lower, next_upper));

        return diff;
    }

  public:
    int maxAncestorDiff(TreeNode *root) {
        auto default_bound = root != nullptr ? root->val : 0;
        return maxAncestorDiff(root, default_bound, default_bound);
    }
};