Implement function to merge two sorted linked lists

merge.c

@@ -0,0 +1,35 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     struct ListNode *next;
+ * };
+ */
+
+struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2) {
+    // Create a dummy node to simplify handling the head
+    struct ListNode dummy;
+    struct ListNode* tail = &dummy;
+    dummy.next = NULL;
+
+    // Traverse both lists
+    while (list1 != NULL && list2 != NULL) {
+        if (list1->val < list2->val) {
+            tail->next = list1;
+            list1 = list1->next;
+        } else {
+            tail->next = list2;
+            list2 = list2->next;
+        }
+        tail = tail->next;
+    }
+
+    // Attach remaining nodes
+    if (list1 != NULL) {
+        tail->next = list1;
+    } else {
+        tail->next = list2;
+    }
+
+    return dummy.next;
+}