Checkpoint: STL in Combination

top_k is the module's exam: it needs a counting map, an ordering, and a tie-break — all three from this module's lessons.

• counting: std::map<std::string, int> with operator[]'s insert-then-increment
• ordering: count descending
• tie-break: lexicographic (smaller word first) — decide this BEFORE coding

Sorting a vector of (count, word) pairs with a comparator that checks count != count first is the cleanest deterministic form. A priority_queue with the same comparator works equally well.

If your tie-break test fails while the basic test passes, your comparator is silently depending on map iteration order or input order — exactly the nondeterminism this course is training you to eliminate.