Counting Grand Tours
Count the Hamiltonian paths (visiting every node exactly once) in an undirected graph; a path and its reverse count as two.
Input: the first line has N and M; each of the next M lines has an edge u v.
Output: the number of Hamiltonian paths.
Constraints:
- 2 ≤ N ≤ 14
- 0 ≤ M ≤ N(N−1)/2
Sample Tests
Input 1
3 3 1 2 2 3 1 3
Output 1
6
Input 2
2 1 1 2
Output 2
2
Discussion (opens after you solve — no spoilers before)
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