I am trying to write a method in Ruby that takes an array of size N and finds duplicates in the array and lists the duplicate.
I'm having trouble creating an array with a range of 0..N-2.
It tells me N is an uninitialized constant. How do I create such an array?
Here's one option
def list_duplicates(array)
duplicates = array.select { |e| array.count(e) > 1 }
duplicates.uniq
end
I tested it out here
list_duplicates([1,1,4,5,6,6,9]
=> [1,6]
array.count iterates over all the elements in the array, just as select does, so for an array of 500K elements, this could be cripplingly slow, as it'd do 250 billion operations. A one-pass approach using group_by might be faster here.You can always use a simple counter hash:
def duplicate_count(array)
array.each_with_object(Hash.new(0)) do |value, hash|
# Keep a count of all the unique values encountered
hash[value] += 1
end.count do |(value,count)|
# Compute how many have a count > 1
count > 1
end
end
duplicate_count([1,2,3,4])
# => 0
duplicate_count([1,2,2,3,4,4,2])
# => 2
If you'd prefer to return the duplicated values:
def duplicate_count(array)
array.each_with_object(Hash.new(0)) do |value, hash|
# Keep a count of all the unique values encountered
hash[value] += 1
end.each_with_object([ ]) do |(value,count), result|
# Collect those with count > 1 into a result array.
if (count > 1)
result << value
end
end
end
You can write following code
def duplicate_value(array)
array.select{|v| array.count(v) > 1}.uniq
end
duplicate_value([1, 2, 1, 3, 3])
=> [1, 3]
I just wrote this, it works and I would like feedback so I'm sharing here.
def duplicate_array(arr)
duplicates = []
while arr.size != 1
pivot = arr.shift
arr.each do |element|
if element.eql?(pivot)
next if duplicates.include?(element)
duplicates << element
end
end
end
duplicates
end
