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Project 1: Bubble Sort

Sorting algorithms are some of the earliest that you typically get exposed to in Computer Science. It may not be immediately obvious how important they are, but it shouldn't be hard to think of some examples where your computer needs to sort some massive datasets during everyday operations.

One of the simpler (but more processor-intensive) ways of sorting a group of items in an array is bubble sort, where each element is compared to the one next to it and they are swapped if the one on the left is larger than the one on the right. This continues until the array is eventually sorted.

Check out this video from Harvard's CS50x on Bubble Sort.

There's also an entry on Bubble Sort on Wikipedia that's worth taking a look at.

Assignment 1

  • Build a method #bubble_sort that takes an array and returns a sorted array. It must use the bubble sort methodology (using #sort would be pretty pointless, wouldn't it?).
> bubble_sort([4,3,78,2,0,2])
=> [0,2,2,3,4,78]
  • Now create a similar method called #bubble_sort_by which sorts an array by accepting a block. Remember to use yield inside your method definition to accomplish this. The block will have two arguments that represent the two elements of the array that are currently being compared. The block’s return will be similar to the spaceship operator you learned about before: If the result of the block execution is negative, the element on the left is “smaller” than the element on the right. 0 means both elements are equal. A positive result means the left element is greater. Use the block’s return value to sort your array. Test your method with the example below.
  > bubble_sort_by(["hi","hello","hey"]) do |left,right|
  >   left.length - right.length
  > end
  => ["hi", "hey", "hello"]

Student Solutions

Submit a link below to this file on the ruby course github repo with your files in it by using a pull request. See the section on Contributing for how.

Show Student Solutions

Project 2: Enumerable Methods

You learned about the Enumerable module that gets mixed into the Array and Hash classes (among others) and provides you with lots of handy iterator methods. To prove that there's no magic to it, you're going to rebuild those methods.

Assignment 2

  1. Create a script file to house your methods and run it in IRB to test them later.
  2. Add your new methods onto the existing Enumerable module. Ruby makes this easy for you because any class or module can be added to without trouble ... just do something like:
  module Enumerable
    def my_each
      # your code here
    end
  end
  1. Create #my_each, a method that is identical to #each but (obviously) does not use #each. You'll need to remember the yield statement. Make sure it returns the same thing as #each as well.
  2. Create #my_each_with_index in the same way.
  3. Create #my_select in the same way, though you may use #my_each in your definition (but not #each).
  4. Create #my_all? (continue as above)
  5. Create #my_any?
  6. Create #my_none?
  7. Create #my_count
  8. Create #my_map
  9. Create #my_inject
  10. Test your #my_inject by creating a method called #multiply_els which multiplies all the elements of the array together by using #my_inject, e.g. multiply_els([2,4,5]) #=> 40
  11. Modify your #my_map method to take a proc instead.
  12. Modify your #my_map method to take either a proc or a block. It won't be necessary to apply both a proc and a block in the same #my_map call since you could get the same effect by chaining together one #my_map call with the block and one with the proc. This approach is also clearer, since the user doesn't have to remember whether the proc or block will be run first. So if both a proc and a block are given, only execute the proc.

Quick Tips:

  • Remember yield and the #call method.

Student Solutions

Submit a link below to this file on the ruby course github repo with your files in it by using a pull request. See the section on Contributing for how.

Show Student Solutions

Additional Resources

This section contains helpful links to other content. It isn't required, so consider it supplemental for if you need to dive deeper into something.