Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
30500	THE HONEYCOMB MAZE	16	631	17 15
5151	Alice’s Cube	8	501	24 21
4556	Think I will Buy Me a Football Team	30	2164	7 11
780	The Archipelago		36	45 34
3377	A Bug’s Life	341	15128	12 13
40642	Chips Challenge	1	22	17 17
34483	Connected country	14	536	6 4
34409	Disconnected country	1	44	34 34
3978	Distance Query	68	1634	24 21
30116	Can you draw it or not?	16	193	5 9
37922	See you again?	3	50	12 12
1674	The Explosion		152
3133	Here We Go(relians) Again	3	168	12 12
11839	Graphic Sequence	1	49	17 23
37921	Birthday Present	3	37	42 34
37375	Kingdom of Equality	2	10	26 26
2670	Count Minimum Spanning Trees	4	175	28 39
4839	Ant	3	190	23 28
215	Panic in the Plazas		82	34 34
5732	Paradox	42	1218	16 19
6288	Treeramids	15	1088	20 17
913	Query on a tree II	115	4358	24 21
3724	Rainbow Ride	8	477	19 19
40639	Escape the New America	1	23	34 34
3405	Almost Shortest Path	80	1660	22 21
3643	Traffic Network	89	2088	18 21
23132	Travelling cost	39	1593	10 8
34565	Tetrahedrons in the country	4	49	17 23
18458	Very Friends 2	4	37	23 23
18457	Very Friends	6	241	11 30
666	Con-Junctions	32	980	14 19
41	Play on Words	42	3198	21 24
6294	Yodaness Level	74	3512	15 16

#graph-theory

The problem involves the study of graphs, which are mathematical structures used to model pairwise relations between objects.

https://en.wikipedia.org/wiki/Graph_theory http://primes.utm.edu/graph/ http://pallini.di.uniroma1.it/ - a program which help with generating graphs http://world.mathigon.org/Graph_Theory http://cs.bme.hu/fcs/graphtheory.pdf - Lecture Notes on Graph Theory