Sphere Online Judge (SPOJ)

list of challenge problems

ID	NAME	QUALITY	USERS	ACC %	DIFFICULTY C I
10295	HQNP Incomputable Hard	3	61	76.53	21 38
18901	The Secret Recipe		45	77.51
758	Tetris AI		74	77.71
2629	Robo Eye	1	39	78.03	34 34
9380	Connecting three towns	2	125	81.06	1 17
7063	Cycles, More Cycles		21	82.50
298	Closing down Railway Lines	3	134	83.36	26 17
18073	Colour Brick Game		55	88.65
11397	Find all independent nodes		26	89.36
11975	PIEK		183	92.17	34 42
11689	Real Roots	1	44	92.48	50 50
12655	Strongly Connected Chemicals		13	95.45