Graph Counting
Time limit5sMemory limit512 MB
Count, modulo 998244353, the non-isomorphic undirected graphs on 2n vertices that have no perfect matching but lose that property when any missing edge is added.
- Level
Hard9 of 10
- Topics
- Combinatorics, Graph, Math, Number theory
- Solved
- No attempts yet
Problem
Consider undirected graphs on 2n vertices with no loops and no multiple edges. A graph G is good if G has no perfect matching, but adding any edge not in G to G produces a graph that has a perfect matching.
Calculate the number of different good graphs on 2n vertices modulo 998 244 353.
Two graphs are different if they are non-isomorphic, meaning that one graph cannot be transformed into the other by relabeling the vertices.
Input
The first line contains one integer n (1 ≤ n ≤ 500 000). Here 2n is the number of vertices in the graph.
Output
Print one integer: the number of different good graphs on 2n vertices modulo 998 244 353.
Hint
Graphs for 2n = 4:
