TODOs

[AnonMiraj]

• add code for cycle detection like Brent or Floyd's tortoise
• improve the code for dfs and bfs and use a lambda instead
• http://tutorial.math.lamar.edu/pdf/Algebra_Cheat_Sheet.pdf
• add hash related stuff
• improve the segtree stuff
• add more TODOs
• add ordered set & ordered multiset
• manacher (https://www.youtube.com/watch?v=nbTSfrEfo6M)
• add binary lifting