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CSES 1690 - Bitmask DP.
Problem: There are cities with one-way flights. Count the number of routes from city to city that visit every city exactly once.
Link: CSES 1690
Constraints:
Note: This is Hamiltonian path counting. The small suggests bitmask DP. The state is (current city, set of visited cities). Transition: move to an adjacent unvisited city and add it to the visited set.
