diff --git a/cpp/more/0021.cpp b/cpp/more/0021.cpp
new file mode 100644
index 0000000..2866171
--- /dev/null
+++ b/cpp/more/0021.cpp
@@ -0,0 +1,48 @@
+#include <cstdio>
+
+/**
+ * Definition for singly-linked list.
+ */
+struct ListNode {
+	int val;
+	ListNode* next;
+
+	explicit ListNode(int x = 0, ListNode* next = nullptr) : val(x), next(next) {}
+};
+
+class Solution {
+public:
+	static ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+		ListNode node;
+		ListNode* ptr = &node;
+		while (list1 && list2) {
+			if (list1->val < list2->val) {
+				list1 = (ptr->next = list1)->next;
+			} else {
+				list2 = (ptr->next = list2) ->next;
+			}
+			ptr = ptr->next;
+		}
+		ptr->next = list1 ? list1 : list2;
+		return node.next;
+	}
+};
+
+ListNode* construct(int x) {
+	return new ListNode(x);
+}
+
+template<typename... Ts>
+ListNode* construct(int x, Ts... xs) {
+	return new ListNode(x, construct(xs...));
+}
+
+int main() {
+	ListNode* list1 = construct(1, 2, 4);
+	ListNode* list2 = construct(1, 3, 4);
+	ListNode* head = Solution::mergeTwoLists(list1, list2);
+	for (ListNode* ptr = head; ptr; ptr = ptr->next) {
+		std::printf("%d ", ptr->val);
+	}
+	return 0;
+}
diff --git a/cpp/more/CMakeLists.txt b/cpp/more/CMakeLists.txt
index 1241580..3dd6e05 100644
--- a/cpp/more/CMakeLists.txt
+++ b/cpp/more/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(more)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(more 0344.cpp)
+ADD_EXECUTABLE(more 0021.cpp)