cpp: add “1026. Maximum Difference Between Node and Ancestor”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cpp/maximum-difference-between-node-and-ancestor.cpp

@@ -0,0 +1,39 @@
+#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);
+    }
+};