updating checkpoint 3

labs/07_list_implementation/README.md

@@ -36,7 +36,25 @@ Linked List of NodeB nodes: 1 -> 1.41421 -> 1.73205 -> 2 -> 2.23607 -> nullptr
 
 **To complete this checkpoint**, show a TA the implementation and the output of your program.
 
-## Checkpoint 3: Debugging a Merge Sort program. 
+## Checkpoint 3: Merge Two Lists. 
+*estimate: 30-40 minutes*
+
+Given two doubly-linked lists: linked list A and linked list B, and both linked lists are sorted. Data in linked list A is sorted in an ascending order. Data in linked list B is also sorted in an ascending order. Merge these two lists such that the data in the merged list is still sorted in an ascending order.
+
+More specifically, complete the mergeLists() function in [checkpoint3.cpp](checkpoint3.cpp), such that the program prints the following output.
+
+```console
+$ g++ checkpoint3.cpp
+$ ./a.out
+1 3 5 7 9
+2 4 6 8 10
+1 2 3 4 5 6 7 8 9 10
+10 9 8 7 6 5 4 3 2 1
+```
+
+**To complete this checkpoint**, explain to a TA your implementation and show the output of your program.
+
+<!--## Checkpoint 3: Debugging a Merge Sort program. 
 *estimate: 30-40 minutes*
 
 We expect our program [checkpoint3.cpp](checkpoint3.cpp) to produce the following results when it is compiled and run.
@@ -54,4 +72,4 @@ Sorted Vector: 2 3 4 7 8
 
 But this program currently does not behave as expected. Troubleshoot this program, find the problems and fix them. You can use a debugger.
 
-**To complete this checkpoint**, explain to a TA the bugs you found, show a TA your fixes and run the program to show that your fixes are correct and the program now produces the expected results.
+**To complete this checkpoint**, explain to a TA the bugs you found, show a TA your fixes and run the program to show that your fixes are correct and the program now produces the expected results.-->