Maximum Difference Between Node and Ancestor
<p>Given the <code>root</code> of a binary tree, find the maximum value <code>v</code> for which there exist <strong>different</strong> nodes <code>a</code> and <code>b</code> where <code>v = |a.val - b.val|</code> and <code>a</code> is an ancestor of <code>b</code>.</p>

<p>A node <code>a</code> is an ancestor of <code>b</code> if either: any child of <code>a</code> is equal to <code>b</code>&nbsp;or any child of <code>a</code> is an ancestor of <code>b</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1000-1099/1026.Maximum%20Difference%20Between%20Node%20and%20Ancestor/images/tmp-tree.jpg" style="width: 400px; height: 390px;" />
<pre>
<strong>Input:</strong> root = [8,3,10,1,6,null,14,null,null,4,7,13]
<strong>Output:</strong> 7
<strong>Explanation: </strong>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.</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1000-1099/1026.Maximum%20Difference%20Between%20Node%20and%20Ancestor/images/tmp-tree-1.jpg" style="width: 250px; height: 349px;" />
<pre>
<strong>Input:</strong> root = [1,null,2,null,0,3]
<strong>Output:</strong> 3
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[2, 5000]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
</ul>
Tree; Depth-First Search; Binary Tree
/**
 * 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 {
public:
    int maxAncestorDiff(TreeNode* root) {
        int ans = 0;
        function<void(TreeNode*, int, int)> dfs = [&](TreeNode* root, int mi, int mx) {
            if (!root) {
                return;
            }
            ans = max({ans, abs(mi - root->val), abs(mx - root->val)});
            mi = min(mi, root->val);
            mx = max(mx, root->val);
            dfs(root->left, mi, mx);
            dfs(root->right, mi, mx);
        };
        dfs(root, root->val, root->val);
        return ans;
    }
};