[] Initial commit. Original version of assignment week 2.

G580|Luna|IDEA12
[] Add solution for 2.1 and unit tests.

G580|Luna|IDEA12
[] Optimize solution for 2.1.

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[] Fix a bug for 2.1, add unit tests to 'protect' it.

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[] Finish 2.2. Assignments for week 2 completes. The use of _ is really nice(see comments on the code for details).

G580|Luna|IDEA12