diff --git a/2112/211231.cpp b/2112/211231.cpp
new file mode 100644
index 0000000..3d2ea01
--- /dev/null
+++ b/2112/211231.cpp
@@ -0,0 +1,44 @@
+#include <iostream>
+
+/**
+ * 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) {}
+	~TreeNode() { delete this->left; delete this->right; }
+};
+
+class Solution {
+private:
+	static int dfs(const TreeNode* const node, int L, int R) {
+		int LDist = (L - node->val) >= 0 ? (L - node->val) : (node->val - L);
+		int RDist = (R - node->val) >= 0 ? (R - node->val) : (node->val - R);
+		int mid, ret = LDist > RDist ? LDist : RDist;
+		int nL = L < node->val ? L : node->val, nR = R > node->val ? R : node->val;
+		if (node->left) {
+			mid = dfs(node->left, nL, nR);
+			ret = ret > mid ? ret : mid;
+		}
+		if (node->right) {
+			mid = dfs(node->right, nL, nR);
+			ret = ret > mid ? ret : mid;
+		}
+		return ret;
+	}
+public:
+	static int maxAncestorDiff(const TreeNode* const root) {
+		return dfs(root, root->val, root->val);
+	}
+};
+
+int main() {
+	// TreeNode root(1, nullptr, new TreeNode(2, nullptr, new TreeNode(0, new TreeNode(3), nullptr)));
+	TreeNode root(8, new TreeNode(3, new TreeNode(1), new TreeNode(6, new TreeNode(4), new TreeNode(7))), new TreeNode(10, nullptr, new TreeNode(14, new TreeNode(13), nullptr)));
+	std::printf("%d\n", Solution::maxAncestorDiff(&root));
+	return 0;
+}
diff --git a/2112/CMakeLists.txt b/2112/CMakeLists.txt
index cfa70b3..4007bce 100644
--- a/2112/CMakeLists.txt
+++ b/2112/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2112)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2112 211230.cpp)
\ No newline at end of file
+ADD_EXECUTABLE(2112 211231.cpp)
\ No newline at end of file