Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
30500	THE HONEYCOMB MAZE	16	642	17 15
5151	Alice’s Cube	8	509	24 21
4556	Think I will Buy Me a Football Team	30	2184	7 11
780	The Archipelago		37	34 26
3377	A Bug’s Life	342	15682	12 13
40642	Chips Challenge	1	23	17 17
34483	Connected country	15	561	5 5
34409	Disconnected country	1	47	34 34
3978	Distance Query	70	1832	24 21
30116	Can you draw it or not?	16	200	5 9
37922	See you again?	3	53	12 12
1674	The Explosion		154
3133	Here We Go(relians) Again	3	170	12 12
11839	Graphic Sequence	1	55	17 23
37921	Birthday Present	3	39	42 34
37375	Kingdom of Equality	2	13	26 26
2670	Count Minimum Spanning Trees	4	188	28 39
4839	Ant	3	193	23 28
215	Panic in the Plazas		83	34 34
5732	Paradox	43	1240	16 19
6288	Treeramids	16	1092	21 19
913	Query on a tree II	117	4653	23 21
3724	Rainbow Ride	8	489	19 19
40639	Escape the New America	3	32	17 17
3405	Almost Shortest Path	79	1687	22 21
3643	Traffic Network	89	2109	18 21
23132	Travelling cost	39	1632	10 8
34565	Tetrahedrons in the country	5	53	17 26
18458	Very Friends 2	4	39	23 23
18457	Very Friends	6	246	11 30
666	Con-Junctions	32	996	14 19
41	Play on Words	43	3282	21 24
6294	Yodaness Level	74	3560	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