7/14/20 practice problems

Question 1

Nested Sum

Define a method, #nested_sum, that takes a 2d_array and returns the sum of all nested elements

Answer 1

def nested_sum(matrix)
   sum = 0
   matrix.each do |med| #slow loop
     med.each do |fast| # med loop
       sum += fast
     end
   end

return sum

 end
 my_matrix = [
   [1, 2],
   [3, 4]
 ]
 p nested_sum(my_matrix) # => 10

Question 2

# Define a method, #pair_product?, that accepts two arguments: an array of
# integers and a target_product (an integer). The method returns a boolean
# indicating whether any pair of elements in the array multiplied together equals
# that product. You cannot multiply an element by itself. An element on its
# own is not a product.

Answer 2

def pair_product?(arr, target_product)

  pairs = []
  arr.each_with_index do |num1, idx1|
    arr.each_with_index do |num2, idx2|
      if idx2 > idx1 && num1 * num2 == target_product
        pairs << [num1, num2]
        print pairs
        puts
        return true
      end
    end
  end

return false

end
p pair_product?([3, 1, 6], 15) # => false
p pair_product?([3, 1, 6], 9) # => false
p pair_product?([3, 1, 6], 18) # => true
p pair_product?([3, 5, 6], 15) # => false
p pair_product?([3, 5, 6], 30) # => false
p pair_product?([3, 5, 6], 17) # => true

Question 3

given a string, return all possible substrings

Answer 3

# def substrings(str)
# end
# p substring("abc")

Question 4

given a string, return the longest substring that is the same forwards and backwards (minimum length 3)

Answer 4

# def longest_palindrome(str)
# end
# p longest_palindrome("abracadabra") # => "aca"
# p longest_palindrome("i sleep in a racecar bed") # => " racecar "

Question 5

# given a gap, return the the first pair of contiguous primes with that gap between them
# primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...

Answer 5

# primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...
# def prime_gap(gap)
# end
# p prime_gap(2) # => [3, 5]
# p prime_gap(4) # => [7, 11]
# p prime_gap(6) # => [23, 29]