Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
30500	THE HONEYCOMB MAZE	16	645	17 15
5151	Alice’s Cube	8	513	24 21
4556	Think I will Buy Me a Football Team	30	2184	7 11
780	The Archipelago		38	34 26
3377	A Bug’s Life	343	15741	12 13
40642	Chips Challenge	1	23	17 17
34483	Connected country	15	566	5 5
34409	Disconnected country	1	48	34 34
3978	Distance Query	70	1873	24 21
30116	Can you draw it or not?	16	200	5 9
37922	See you again?	3	55	12 12
1674	The Explosion		155	17 17
3133	Here We Go(relians) Again	3	170	12 12
11839	Graphic Sequence	1	55	17 23
37921	Birthday Present	3	40	42 34
37375	Kingdom of Equality	2	13	26 26
2670	Count Minimum Spanning Trees	4	188	28 39
4839	Ant	3	192	23 28
215	Panic in the Plazas		84	34 34
5732	Paradox	43	1239	16 19
6288	Treeramids	16	1093	21 19
913	Query on a tree II	117	4678	23 21
3724	Rainbow Ride	8	491	19 19
40639	Escape the New America	3	33	17 17
3405	Almost Shortest Path	79	1692	22 21
3643	Traffic Network	89	2109	18 21
23132	Travelling cost	39	1635	10 8
34565	Tetrahedrons in the country	5	53	17 26
18458	Very Friends 2	4	39	23 23
18457	Very Friends	6	247	11 30
666	Con-Junctions	32	999	14 19
41	Play on Words	43	3289	21 24
6294	Yodaness Level	74	3563	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