chore: import upstream snapshot with attribution

data_structures/cll/main_cll.cpp

@@ -0,0 +1,43 @@
+#include "cll.h"
+using namespace std;
+
+int main() {
+    /* Test CLL */
+    cout << "----------- Test construct -----------" << endl;
+    cll list1;
+    list1.display();
+    cout << "----------- Test insert front -----------" << endl;
+    list1.insert_front(5);
+    cout << "After insert 5 at front: " << endl;
+    list1.display();
+    cout << "After insert 10 3 7 at front: " << endl;
+    list1.insert_front(10);
+    list1.insert_front(3);
+    list1.insert_front(7);
+    list1.display();
+    cout << "----------- Test insert tail -----------" << endl;
+    cout << "After insert 18 19 20 at tail: " << endl;
+    list1.insert_tail(18);
+    list1.insert_tail(19);
+    list1.insert_tail(20);
+    list1.display();
+    cout << "----------- Test find item -----------" << endl;
+    if (list1.find_item(10))
+        cout << "PASS" << endl;
+    else
+        cout << "FAIL" << endl;
+    if (!list1.find_item(30))
+        cout << "PASS" << endl;
+    else
+        cout << "FAIL" << endl;
+    cout << "----------- Test * operator -----------" << endl;
+    int value = *list1;
+    cout << "Value at *list1: " << value << endl;
+    cout << "----------- Test ++ operator -----------" << endl;
+    list1.display();
+    ++list1;
+    cout << "After ++list1: " << endl;
+    list1.display();
+
+    return 0;
+}