Finding duplicate elements in an array

array_duplicates.rb

#!/usr/bin/env ruby
# Problem: Find the duplicate values in a 1..n array

# CREATE THE PROBLEM

  # Size of the data set
  dataset_size = 100
  # The data set: This will become an array of numbers
  numbers = []

  # Initialize the array of numbers
  (1..dataset_size).each do |n|
    numbers[n] = n
  end
  # Including some duplicate numbers
  numbers[50] = 15
  numbers[52] = 12

# SOLVE THE PROBLEM

  # This array will hold a boolean flag for each number
  discovered = []
  # Holds any results (numbers determined to be duplicates)
  results = []

  # Create an array of false values, where each index can be set to 
  # true if its associated number has been found
  discovered.fill(false, 1..dataset_size)

  # Loop through all numbers in the ideal dataset
  (1..dataset_size).each do |n|
    # If this number has previously been discovered
    if discovered[numbers[n]]
      # then it is a duplicate
      results << numbers[n]
    end
    # Either way, flag this number as discovered
    discovered[numbers[n]] = true
  end

# DISPLAY RESULTS

  puts "Results:"
  results.each do |n|
    puts n
  end