README.md

Installation

Below is the requirement to run this project:

• Ruby: 2.6.1
• Rspec

Circular shift (Rotate bits)

Assumptions

• I assume that we need to specify the bits because with the same number but different bits, the result will be different.
• When user input a number which exceeds the maximum value of bits, it will cause error. For example:

ruby circular_shift.rb -n 256 -b 8 -s 2 -d left

-> NUMBER exceeds the maximum number 255 of 8 bits

• I don't write automated integration test for circular_shift.rb file because it's pretty much the same with testing helpers/bit_helper.rb

Command

To run circular shift, please use the command below:

ruby circular_shift.rb -n NUMBER -b INT_BITS -s STEPS -d DIRECTION

Command usage:

Usage: circular_shift [options]
    -n, --number NUMBER              the NUMBER to be circular shifted
    -b, --bits INTEGER_BITS          the INTEGER BITS of the NUMBER
    -s, --steps STEPS                the number of STEPS that the NUMBER will be circular shifted
    -d, --direction DIRECTION        the DIRECTION that the NUMBER will be circular shifted

Please note that -d default option is left.

Example command:

ruby circular_shift.rb -n 123 -b 8 -s 2 -d left
ruby circular_shift.rb -n 123 -b 8 -s 2 -d right
ruby circular_shift.rb -n 123 -b 8 -s 2

Unit tests

Unit test is located in folder spec/.To run unit test, please use the command below:

# to run all tests
rspec spec

# to run only unit test for circular_shift
rspec spec/helpers/bit_helper_spec.rb

Check balance of parenthesis in a string

Assumptions

• I don't write automated integration test for check_balance_parenthesis.rb file because it's pretty much the same with testing helpers/string_helper.rb

Command

To check balance of parenthesis in a string, please use the command below:

ruby check_balance_parenthesis.rb  -s STRING

Command usage:

Usage: check_balance_parenthesis [options]
    -s, --string STRING              the STRING to be checked

Example command:

ruby check_balance_parenthesis.rb  -s "([{}()])"

Unit tests

Unit test is located in folder spec/.To run unit test, please use the command below:

# to run all tests
rspec spec

# to run only unit test for balance of parenthesis
rspec spec/helpers/string_helper_spec.rb

LRU cache

I study the problem but I don't have enough time to code it properly, with thread safe handling and UT.

Solution

• Theory: https://www.geeksforgeeks.org/lru-cache-implementation/
• Solution:

class LruCache

  def initialize(max_size)
    @max_size = max_size
    @data = {}
  end

  def max_size=(size)
    raise ArgumentError.new(:max_size) if @max_size < 1
    @max_size = size
    if @max_size < @data.size
      @data.keys[0..@[email protected]].each do |k|
        @data.delete(k)
      end
    end
  end

  def [](key)
    found = true
    value = @data.delete(key){ found = false }
    if found
      @data[key] = value
    else
      nil
    end
  end

  def []=(key,val)
    @data.delete(key)
    @data[key] = val
    if @data.length > @max_size
      @data.delete(@data.first[0])
    end
    val
  end

  def each
    @data.reverse.each do |pair|
      yield pair
    end
  end

  # used further up the chain, non thread safe each
  alias_method :each_unsafe, :each

  def to_a
    @data.to_a.reverse
  end

  def delete(k)
    @data.delete(k)
  end

  def clear
    @data.clear
  end

  def count
    @data.count
  end

  # for cache validation only, ensures all is sound
  def valid?
    true
  end
end

cache = LruCache.new(3)
cache[:a] = 1
cache[:b] = 2
cache[:c] = 3
cache[:d] = 4

puts cache
# output should be: [:d,4],[:c,3],[:b,2]

• Our cache should handle thread safe cache too