Finished solving 50 Project Euler problems!!! (http://projecteuler.net/problems) (5/6/2014) Only 5.88%, 40759 out of 693691 software people worldwide, have done this.
Graph algorithms (see my 900 lines of code, with full RSpec tests): https://github.com/rayning0/ProjectEuler-and-Algorithms/tree/master/graph_algorithms RSpec output: https://github.com/rayning0/ProjectEuler-and-Algorithms/blob/master/graph_algorithms/data/rspec_screen_output.txt
CodeEval (https://www.codeeval.com/open_challenges/), and algorithm problems. See /euler, /codeeval, and /algo directories. Please do NOT see my solution for a problem unless you have first tried it yourself.
Also, see my repo on RubyQuiz, InterviewCake, and other challenge questions: https://github.com/rayning0/rubyquiz.
Test-First Ruby problems: https://github.com/rayning0/Test-First-Ruby
App Academy problems: https://github.com/rayning0/App-Academy-Practice-Problems